Spiders and their structure. Class arachnids: external structure. Spider body structure
At the exclamation of "spider", most people will cringe, because they do not associate this word with anything good. The first thing that comes to mind is that spiders are poisonous, and non-poisonous ones are just unpleasant ... they look so strange, and they weave webs in the corners. But one has only to get to know these creatures better and fear will be replaced, if not with delight, then with respect. Few can compare with them in terms of diversity of structure, lifestyle and complexity of behavior. From the point of view of taxonomy, spiders make up a separate order of the class Arachnida, numbering 46,000 species! And this is not a complete list, because new types of spiders continue to be discovered until now. Their closest relatives are ticks, salpugs and scorpions, and their distant ancestors are marine arthropods like relic horseshoe crabs. But with insects, to which spiders are often ranked, they just have nothing in common.
The two-horned spider (Caerostris sexcuspidata), which lives in the arid regions of Africa, imitates a dry tree with the help of body shape, color and posture.
The body of spiders consists of a cephalothorax and abdomen, connected by a so-called stalk. The cephalothorax is usually small, and the abdomen is highly extensible, so it is much larger than the chest. In most species, the stalk is so short that it is almost invisible, but myrmecium spiders, which mimic ants, boast a thin waist.
A spider from the genus myrmecium (Myrmecium sp.) pretends to be an ant, but its cunning is easy to unravel if you count the number of legs.
All spiders have eight legs, and by this feature they can be unmistakably distinguished from insects, which have six. But besides the legs, spiders have several more pairs of limbs. The first, called chelicerae, is located near the mouth. According to their purpose, chelicerae are a cross between mandibles and hands. With their help, spiders grab and cut prey, and also hold the female during mating, cut the web - in a word, they perform delicate types of work. The second pair of limbs are pedipalps. They are also located on the cephalothorax, but are longer and more like legs. This is a specific tool that spiders use to strain the liquid, semi-digested tissues of the victim. Males have special shaped pedipalps that they use to transfer sperm to the female. At the tip of the abdomen, several pairs of limbs have changed and turned into spider warts. Each such wart is connected to a large spider gland located in the abdomen. Spider glands are of different types and each of them produces its own kind of web.
An enlarged portrait of the earthen wolf spider (Trochosa terricola) allows you to delve into the details of spider anatomy: black eyes are visible on the sides of a pair of large eyes; the brown prehensile organs just below the eyes are the chelicerae, and the short, light yellow "legs" are the pedipalps.
All spiders breathe atmospheric oxygen, so their respiratory organs are lungs or tracheas. It is noteworthy that they have 4 lungs (or the same number of tracheas), and there are species that have a pair of both. The digestive system of spiders is relatively simple. Almost all species have venom glands, the secret of which is fatal to their victims, and sometimes to large animals. In prey paralyzed by the toxin, the spider injects saliva containing highly active enzymes. This juice partially digests the tissues of the victim, the hunter can only suck in semi-liquid food. The outer covers of spiders are not extensible, therefore, for uniform growth, they often have to molt. During molting and immediately after it, the spider is defenseless, during this period it does not hunt, but sits in a secluded place.
The dolophones spider (Dolophones sp.) owes its disguise to a protective coloration and pose at the same time.
The most amazing thing about the anatomy of these animals is the sense organs. Compared to other invertebrates in spiders, they are well developed and diverse. The first thing you notice is the eyes. Spiders usually have eight of them, of which the two main ones face forward, and the rest are located on the top and sides of the head, which gives their owner a three-dimensional view of 180 °. True, there are species with six, four and even two eyes, but this is not so important, because all spiders see only light spots (but they distinguish colors!). The exception is stray jumping spiders, which do not weave trapping webs, but attack the victim with “bare hands”. They have developed sharp binocular vision for an accurate throw, which allows them to distinguish clear contours of prey and correctly estimate the distance to it. Cave species of spiders are completely blind.
To overcome the fear of spiders forever, just look into the expressive iridescent eyes of this female jumping spider (there are four of them on the front side). The view shown in the photo - fidippus mystaceus (Phidippus mystaceus) reaches a length of about 1 cm.
The sense of touch is much more important for hunting. It is unprecedentedly sharp in all spiders. Sensitive receptors and hairs on the paws allow them to capture insignificant fluctuations not only of the web, but also of the air itself. We can say that spiders hear with their feet. It has been observed that the sound of the violin awakens the hunting instinct in some spiders. Probably, the vibrations of the air caused by the instrument remind them of the buzzing of a fly. By the way, spiders themselves are by no means voiceless. Large species can hiss, buzz, crackle, apparently to scare off enemies. Small ones sing mating songs, but so quietly that this sound is not perceptible to the human ear, but females hear it perfectly. The sound of spiders arises from the friction of different parts of the body from each other, that is, according to the same principle as that of grasshoppers. But the abilities of spider legs are not limited to this. It turns out that spiders can smell with their feet! In fairness, it must be said that olfactory receptors are also located on the abdomen. The smell is important not so much for the capture of prey, but for procreation. Following the odorous trail of the female, eight-legged knights cover long distances and unmistakably distinguish a mate ready for mating from an immature one. Another sense that spiders have mastered to perfection is the sense of balance. Spiders, without looking, accurately determine where the top is, where the bottom is, which is not surprising for animals that spend most of their lives in limbo. Finally, spiders do not have taste buds, but they do have a taste. They distinguish tasty prey from tasteless prey again with their feet!
Theraphosa blondi female in natural environment.
The sizes of spiders vary widely. The body length of large tarantula spiders reaches 11 cm, one of them - Blond's teraphosa - even got into the Guinness Book of Records with a leg span of 28 cm. Crumb spiders are equally amazing. So, the smallest species - patu digua - grows to only 0.37 mm!
The patu digua spider (Patu digua) is so small that it is difficult to distinguish even at this magnification, when the papillary pattern of a human finger is visible.
Due to the spherical or pear-shaped abdomen, the outlines of the body in most spiders are closer to the circumference. But in nephil orbs, the body is elongated; in some species, the abdomen can be in the shape of a rhombus, heart, or strongly flattened.
A female Gasteracantha cancriformis in her hunting net. This type of spider got its name (loosely translated from Latin as “crab-shaped prickly belly”) for the unusual shape of the body, in contrast to the crab spiders, so named for the ability to move sideways.
Body contours can be distorted by long hairs and spines.
Curved or arched gasteracantha (Gasteracantha arcuata) is a relative of the previous species, but looks even more exotic.
Jumping spiders from the genus Simetha (Simaetha) are tiny (a couple of millimeters in size) inhabitants of the tropics of Southeast Asia. All representatives of this genus wear an outfit with a gold pattern.
The length of the legs also changes. In terrestrial species, it is usually small, and spiders that weave webs and spend a lot of time in the thick of foliage are often long-legged.
The color of these arthropods can be, without exaggeration, any, but given the predatory nature of spiders, it is almost always patronizing. Accordingly, the types of the temperate zone are usually painted inconspicuously: in gray, black, brown tones - to match the earth, sand, dry grass. Tropical spiders are often bright, with complex patterns.
Tweitesia are exceptionally beautiful, whose body is encrusted with shiny spots that look like sequins.
Silver-dotted tweitesia (Thwaitesia argentiopunctata).
In terms of territory coverage, spiders can be safely called cosmopolitans. They live on all continents, in all climatic zones and in all natural environments. Spiders are most diverse in the steppes, meadows and forests, but they can also be found in deserts, tundras, caves, among the glaciers of the Arctic islands and high mountains, in fresh water, human dwellings. By the way, spiders are one of the highest mountain animals - the Himalayan jumping spider lives on Everest at an altitude of 7000 m!
Prey of the Himalayan jumping spider (Euophrys omnisuperstes) - insects brought to Everest by wind.
The habitat has left its mark on the way of life of different species. Common to all spiders is that predation and the associated tendency to loneliness, although there are exceptions. Social filoponella and stegodiphus prefer to build a common network, which they hunt together ...
Saracen stegodiphuses (Stegodyphus sarasinorum) unanimously attack an unlucky butterfly. This species lives in India, Nepal, Myanmar and Sri Lanka.
and Kipling's bagheera jumping spider, contrary to its predatory name, is herbivorous.
Kipling's bagheera (Bagheera kiplingi) carries a bloodless victim in chelicera - juicy appendages that grow on the leaves of some tropical acacias. Trees thus attract ants, which along the way protect them from pests, and the herbivorous spider uses these gifts free of charge.
Most spiders are sedentary, although among the jumping spiders and wolf spiders there are many vagrants who freely roam the open spaces and attack oncoming insects of a suitable size. Homebody species are equipped in different ways. The most primitive of them hide from prying eyes in the recesses of the soil: it is more convenient to hunt and defend themselves. Sidewalk spiders (crab spiders) hide among the petals of flowers, while sitting on one flower, they gradually change color to match their shelter.
What could be more idyllic than a butterfly drinking nectar? But a tragedy is unfolding before us: the beauty actually fell into the paws of a side-walker spider, indistinguishable in color from the flower on which it hunts.
But a good disguise does not solve all problems, because it is not enough to grab a victim, you also need to keep it, and it’s tiring to look out for prey for days on end. Therefore, spiders gradually moved from active ambush hunting to more reliable and passive methods of catching prey. At the first stage, they began to dig deep minks, lining them with cobwebs for greater convenience.
The trapping tube of the Rechenberg cebrennus (Cebrennus rechenbergi) is woven from cobwebs, inlaid on the outside with grains of sand.
More advanced species began to stretch the threads from the mink to neighboring stems - an ideal notification system turned out: the owner can rest in the mink, and the crawling insect, having hooked the cobweb, will notify the spider of its approach and will be taken by surprise by the sudden appearance of a predator from under the ground. In some species, such signaling threads have evolved into complex arachnoid funnels and tubes.
Other species began to improve not the warning system, but the methods of retaining prey. To do this, they began to close the minks with earthen plugs and not simple ones, but on hinges! The spider, sitting on the inside of the hatch, keeps it closed, so that it is completely impossible to see its dwelling from the surface. As soon as the victim hooks on the signal web, the spider jumps out, drags the stunned insect into the hole, slams the lid and paralyzes with a bite. In this scenario, even strong prey has no chance to escape.
An open spider burrow with a raised lid and signal cobwebs stretching in all directions.
However, burrow hunting does not allow spiders to get off the ground, so the most advanced species stopped equipping dens and began to be content with only one web, stretching it among grass, leaves and other above-ground objects.
Creating a web, the spider places it in the places of the most probable movement of prey, but so that gusts of wind, vibrations of branches, and movements of large animals do not break it.
The fact is that spiders spend a lot of deficient protein to create a web, so they value this material. They often eat a torn web, using it as a raw material for the production of a new one. The structure of the web ideally takes into account the characteristics of the favorite prey of one or another type of spider: in one case, it can be randomly stretched threads in all directions, in the other, a circle sector stretched in the corner of the shelter, in the third, a full circle.
Rainbow play of light on a circular web stretched in the gorge of the Karijini National Park (Australia).
A thin cobweb seems fragile, but in terms of the thickness of the thread, this is one of the strongest fibers on Earth: a cobweb with a conditional thickness of 1 mm can withstand a weight of 40 to 261 kg!
Drops of water are much larger in diameter than cobwebs, but cannot break them. When they dry, the web, due to its elasticity, will restore its shape.
In addition, the web is very elastic (it can stretch to a third of its length) and sticky, so the beating victim with its movements only confuses itself even more. The web of nephil orbs is so strong that it can even hold a bird.
A tern entangled in the web of a nephila orbworm in the Seychelles. From the side of the spider, nothing threatens her, since the bird is too big for him. Usually in such cases, the nephiles simply cut off the cobwebs so that the beating prey does not spoil the entire network for them. However, the sticky web sticks the feathers together, which can cause the bird to lose its ability to fly and die of starvation.
Some spiders additionally strengthen the web with special threads - stabiliments.
The North American spider Uloborus glomosus (Uloborus glomosus) has reinforced its web in a spiral with zigzag stabiliments.
It is difficult to imagine the creator of the web outside the air, but among the spiders there were also such. Spiders from the genus of hunters roam among coastal vegetation in search of near-water insects, but on occasion they easily move along the surface of the water and even plunge into its thickness, holding on to plants.
When crossing a pond, the banded hunter (Dolomedes fimbriatus), like water strider bugs, rests on a film of water tension.
The water spider does not leave the reservoir at all; among the underwater vegetation, it creates a dome of cobwebs, from which it stretches trapping threads. The body of this spider is covered with hairs that hold air bubbles. The spider periodically rises to the surface in order to renew their supply, and drags large bubbles with it and fills the space under the dome with them. In this air tent he lives and breeds.
Water spider (Argyroneta aquatica) and the air bell he created. The body of the spider itself is also surrounded by an air bubble, giving it a silvery hue.
Spiders breed in the tropics all year round, in the temperate zone - once a year, in summer. Usually, male spiders are much smaller than females (in some species, 1500 times!), Less often - almost the same size as them, and only in a water spider, males are a third larger than their girlfriends. In addition to size, males, as a rule, are also distinguished by bright colors. Mating in these arthropods occurs unusually - without direct contact of the genitals. First, the male fills the pedipalps with sperm and sets off on a journey with this gift. Having followed the trail of the female by smell, he proceeds to solve the main problem: how to get close to the gluttonous and huge girlfriend without awakening her hunting instinct? Different species follow different strategies. Some spiders warn of their appearance with a characteristic twitching of the web - this “call” should make it clear to the female that there is no prey in front of her, but it does not always work, and often the boyfriend has to flee at full speed. Other males build a small mating net next to the female's web: rhythmically twitching it, they invite their girlfriend to a closer acquaintance. Male wandering spiders, which do not weave webs, perform a mating dance, raising their paws in a certain sequence, like traffic controllers. In some species, daredevils manage to involve the spider in the dance. Males of the amazing Pisaura (Pisaura mirabilis) rely on a tried and tested trick: they go on a date with a treat - a fly wrapped in a web. The most timid of spiders mate only with a recently molted female: with soft covers, she herself is defenseless and not prone to attack. During mating, the male introduces pedipalps into the female's spermatic tract, sometimes entangling her with cobwebs as a safety net.
Acrobatic sketch performed by a male peacock spider. In addition to raising their legs, males of all species of this genus also show an unusually colorful abdomen, raising it like a peacock's tail. It is almost impossible to see this miracle in nature, since the size of peacock spiders is only a couple of millimeters.
Usually an intimate meeting takes place in private, but sometimes several males look after one female and then they arrange fights among themselves. It happens that the female mates successively with several males. After mating, the spider often eats one or all partners. In some species, males survive by agile flight or cunning.
The male flower spider (Misumena vatia) climbed onto the back of the female and became inaccessible to her. For him, this is the only way to protect himself after mating, since the forces of the partners are too unequal. Some types of cross-spiders use the same method.
In more rare cases, the male and female part peacefully or even live in the same nest, sharing prey. A few days or weeks after mating, the female lays her eggs in a webbed cocoon.
The cocoon of the brown agreca (Agroeca brunnea) is two-chambered: in the upper chamber there are eggs, and in the lower chamber there are nurseries for newborn spiders.
The fertility of different species varies from 5 to 1000 eggs, if there are many eggs, then there can be up to a dozen cocoons. The size of the cradle is small - from a couple of millimeters to 5 centimeters in diameter; coloring can be white, pink, green, golden, striped.
Gasteracantha cancriformis cocoons are as unusual as these spiders themselves. The females attach their golden-black-striped cradles to the underside of the leaves.
If in relations with males spiders demonstrate the dark side of their nature, then in dealing with offspring they show the light side. Females carefully attach cocoons in a secluded corner of the hunting net, their own nest, burrow, and vagrant species carry them with them, holding them with chelicerae or gluing them to the abdomen. Females of the Venezuelan cross (Araneus bandelieri) weave a common cocoon, and some species, like cuckoos, throw their offspring into the nests of their neighbors. If the cocoon is left in a secluded place, then after hatching, the spiders are left to their own devices. Until the expiration of the first three molts, they keep crowded, and then disperse. Females carrying cocoons with them often take care of their offspring and after birth they are spiderlings. They carry babies on their bodies and provide food.
Female of one of Pisaura species (Pisaura sp.) with a precious burden glued to her abdomen.
Young spiders living in open landscapes often resort to settling with the help of a web. To do this, they climb a stalk or twig higher and release a cobweb, but do not attach it as when weaving a net, but leave it to hang free. When the thread is long enough, the wind picks it up along with the spider and takes it far, sometimes over a hundred kilometers. The years of such a web are especially noticeable in August-September.
Web with a brood of spiders. While the kids are small, they keep crowded.
In species of the temperate zone, wintering often takes place in the egg stage, but if young spiders hibernate, they often demonstrate resistance to cold and can appear on the snow during winter thaws. Most small spiders live no more than a year, the largest tarantulas in nature live up to 7-8 years, and all 20 can live in captivity.
This is not snow, but a carpet of cobwebs that covers the shore of one of Australia's reservoirs.
The prey of spiders is varied. First of all, their victims are mobile, but not too strong insects - flies, mosquitoes, butterflies - they are the ones who have the greatest chance of getting into the net.
If the victim is especially slow and defenseless, then the spider does not hesitate to attack prey many times larger than itself: a caterpillar, an earthworm, a snail.
Nomadic species and spiders that live in minks are more likely to come across flightless beetles and orthoptera.
Hutchinson's Mastophora (Mastophora hutchinsoni) uses a very unusual way of hunting. She weaves a gossamer with a sticky drop at the end, hangs with this boladoras in an outstretched paw and swings it until some insect sticks to the drop.
The largest tarantulas prey mainly on small vertebrates - lizards, snakes, frogs. Occasionally, small birds (more often chicks) become their prey, which is reflected in their name and at the same time gave rise to a prejudice that tarantulas eat only birds.
Deinopis spiders (Deinopis sp.) first weave a square net, and then, holding it straight, creep up and throw it on prey.
Amphibiotic and water spiders catch tadpoles, aquatic insect larvae, fish fry and even adult small fish. Some species of spiders have a narrow food specialization, for example, they hunt only ants or spiders of other species.
Large vertebrates are never attacked by spiders, but some venomous spiders may bite in self-defense. Spider venom can be of local and general action. Local venom causes severe pain at the site of the bite, redness (blue), swelling and tissue death, in some cases so deep that internal organs are exposed. A general venom causes headache, nausea, vomiting, convulsions, mental agitation, skin rash, palpitations, kidney dysfunction, in severe cases, suffocation and death. Fortunately, most poisonous spiders belong to tropical exotics, and of those common in densely populated areas, the South Russian tarantula and karakurts are the most dangerous.
The South Russian tarantula (Lycosa singoriensis), although infamous, is not as dangerous as the karakurt.
These spiders live in the herbage of the steppes and semi-deserts of Southern Europe, Asia and North America, and livestock also suffer from their bites, which in the past sometimes led to a mass death of grazing camels, sheep, and horses. The venom of the karakurt is 15 times stronger than the venom of the gyurza, but unlike the snake, the bite of the spider is shallow, therefore, as a first aid, cauterization of the bite site with a burning match is effective. True, this measure is saving only in the case of immediate (within 1-2 minutes) application. If first aid was not provided, then the victim's life can only be saved in the hospital with the help of anti-karakurt serum.
The female karakurt (Latrodectus tredecimguttatus) guards cocoons with eggs, during this period she is especially aggressive. The species shown in the photo lives in arid regions of Europe and Asia.
Although spiders seem to be dangerous and invulnerable predators, they are defenseless against many enemies. They are hunted by all kinds of birds, small animals, lizards, frogs. Bustards, noses and dormouse do not give in even to poisonous species: birds fill their stomachs with karakurts, and animals hunt tarantulas. Among the invertebrates there are also brave men who are ready to eat their eight-legged brother. Spiders are attacked by praying mantises, bears, predatory beetles and even ... flies, however, not ordinary, but predatory.
These female scorpion spiders (Arachnura melanura) display a variety of intraspecific coloration. Females of this species have an elongated abdomen, which they can move like scorpions. Despite their formidable appearance, they do not have a sting, and the bite of these spiders is painful, but not dangerous. Males are smaller and of a regular shape.
Dead tarantula infected with cordyceps. Outgrowths that look like deer antlers are the fruiting bodies of the fungus.
This Thai argiope (Argiope sp.) sits in a trapping net with legs folded in pairs and stretched along the stabiliments. So it becomes part of the web pattern and ceases to interest others.
In this regard, spiders have developed a variety of means of protection (some of them also serve as adaptations for hunting). This should include protective coloring and body shape, as well as special postures.
Some spiders freeze in the center of the web with outstretched legs, becoming like a stick, frinarachns and pasilobuses imitate bird excrement in this position and even emit an appropriate smell that attracts flies!
Seeing danger, nomadic species take to their heels; spiders weaving a web, on the contrary, land on the ground; some species take a threatening posture with their paws raised high; small spiders shake the web so that their contours in the trembling network seem to be blurred.
The sickle-shaped pasilobus (Pasilobus lunatus) is indistinguishable from the excrement of small animals, but it only looks like this in sunlight.
As if as a reward for its unpretentious appearance, nature endowed this spider with the ability to glow in ultraviolet light.
Venomous spiders bite while tarantulas… shaken, while the hairs covering their body break off and rise into the air. When inhaled and on the skin, they cause irritation.
Rechenberg's already familiar cerebrennus never ceases to amaze: in case of danger, he flees, tumbling over his head!
It can only be surpassed by the golden-yellow carparachna living in the Namib Desert.(Carparachne aureoflava), which does not run away from enemies, but rolls head over heels from the dune, developing a speed of up to 1 m / s. This speed is not so small, because in order to reach it, the carparachne must make 40 somersaults over its head!
Paraplektana spider (Paraplectana sp.) dressed as a ladybug.
Some burrow spiders create three-chamber underground shelters to protect against wasps: if the enemy managed to crack the first door, the spider moves to the next compartment of the hole, which is also locked with a lid, and so on. At the same time, burrows can be configured in such a way that the enemy is simply not able to find the spider in the underground labyrinth.
The female of the severed cyclocosmia (Cyclocosmia truncata). This burrow spider, originally from Mexico, uses the most original method of protection - it plugs the entrance to the hole with its own body. The blunt end of the abdomen perfectly matches the size of the hole, so that a perfect cork is obtained, which is very difficult to pull out from the outside.
The front side of the abdomen of the cyclocosmia resembles an ancient seal.
Spiders have long evoked mixed feelings in people. On the one hand, they were feared because of their unpleasant appearance and poisonousness. The infamous karakurt in North America was nicknamed the "black widow", and the word "karakurt" in Kazakh means "black death". The subconscious fear of spiders is so strong that some people, even now, with little or no contact with dangerous species, are terribly afraid of these arthropods - such a mental deviation is called arachnophobia. On the other hand, people have always been fascinated by the ability of spiders to weave webs, and attempts have been made to extract practical benefits from this. Even in ancient China, they knew how to make a special “fabric of the eastern sea” from the web, the Polynesians used a thick web for sewing and making fishing nets. In Europe, in the 18th-19th centuries, isolated attempts were made to make fabric and clothing from cobwebs; in modern industry, cobwebs are used in instrument making. However, it was not possible to give rise to the industrial production of this material due to the difficulties of keeping and breeding a huge number of producers. Now spiders are bred in captivity as exotic pets, and large tarantulas, which are convenient to observe, are most popular among amateurs. But other species of these arthropods also deserve protection as useful and very effective regulators of the number of harmful insects.
Smith's Brachypelma (Brachypelma smithi; female) is one of the most popular tarantula spiders. Due to the massive catch for sale in their homeland, in Mexico, it has become rare.
Read about the animals mentioned in this article: horseshoe crabs, ants, grasshoppers, praying mantises, ladybugs, crabs, snails, frogs, snakes, lizards, peacocks, cuckoos, deer.
And) can reach 20 cm in length. Some tarantulas are even larger.
Traditionally, two sections are distinguished in the body of arachnids - so(cephalothorax) and opisthosoma(abdomen). The prosoma consists of 6 segments each bearing a pair of limbs: chelicerae, pedipalps, and four pairs of walking legs. In representatives of different orders, the structure, development and functions of the limbs of the prosoma differ. In particular, pedipalps can be used as sensitive appendages, serve to capture prey (), act as copulatory organs (). In a number of representatives, one of the pairs of walking legs is not used for movement and takes on the functions of the tactile organs. The segments of the prosoma are tightly connected to each other; in some representatives, their dorsal walls (tergites) merge with each other to form a carapace. The merged tergites of the segments form three scutes: propeltidia, mesopeltidia, and metapeltidia.
The opisthosoma initially consists of 13 segments, the first seven of which may bear modified limbs: lungs, ridge-like organs, arachnoid warts, or genital appendages. In many arachnids, the segments of the prosoma fuse with each other, to the point of losing the outer segmentation in most spiders and mites..
covers
Arachnids have a relatively thin chitinous cuticle, under which lies the hypodermis and basement membrane. The cuticle protects the body from loss of moisture during evaporation, so arachnids inhabited the most arid regions of the globe. The strength of the cuticle is given by proteins that encrust chitin.
Respiratory system
The respiratory organs are the trachea (y, and some) or the so-called lung sacs (y and), sometimes both together (y); the lower arachnids do not have separate respiratory organs; these organs open outward on the underside of the abdomen, less often on the cephalothorax, with one or more pairs of respiratory openings (stigma).
The lung sacs are more primitive structures. It is believed that they occurred as a result of a modification of the abdominal limbs in the process of mastering the terrestrial way of life by the ancestors of arachnids, while the limb was pushed into the abdomen. The lung sac in modern arachnids is a depression in the body, its walls form numerous leaf-shaped plates with extensive gaps filled with hemolymph. Through the thin walls of the plates, gas exchange occurs between the hemolymph and the air entering the lung sac through the openings of the spiracles located on the abdomen. Pulmonary respiration is available in scorpions (four pairs of lung sacs), flagellates (one or two pairs) and low-organized spiders (one pair).
Pseudo-scorpions, haymakers, salpugs, and some ticks have tracheae as respiratory organs, and most spiders (except the most primitive ones) have lungs at the same time (there is only one - the front pair) and trachea. The trachea are thin branching (for harvesters) or non-branching (for pseudoscorpions and ticks) tubules. They penetrate inside the body of the animal and open outwards with holes in the stigmas on the first segments of the abdomen (in most forms) or on the first segment of the chest (in the salpugs). The tracheae are better adapted to air gas exchange than the lungs.
Some small mites have no specialized respiratory organs; in them, gas exchange occurs, like in primitive invertebrates, through the entire surface of the body.
Nervous system and sense organs
The nervous system of arachnids is distinguished by a variety of structures. The general plan of its organization corresponds to the ventral nerve chain, but there are a number of features. The deutocerebrum is absent in the brain, which is associated with the reduction of the appendages of the acron - antennules, which are innervated by this part of the brain in crustaceans, centipedes and insects. The anterior and posterior sections of the brain are preserved - the protocerebrum (innervates the eyes) and the tritocerebrum (innervates the chelicerae).
The ganglia of the ventral nerve cord are often concentrated, forming a more or less pronounced ganglionic mass. In harvestmen and ticks, all ganglia merge, forming a ring around the esophagus, but in scorpions, a pronounced ventral chain of ganglia is preserved.
sense organs arachnids are developed differently. The most important thing for spiders is touch. Numerous tactile hairs - trichobothria - are scattered in large numbers over the surface of the body, especially on the pedipalps and walking legs. Each hair is movably attached to the bottom of a special hole in the integument and is connected to a group of sensitive cells located at its base. The hair perceives the slightest fluctuations in the air or the web, sensitively reacting to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations.
The organs of chemical sense are lyre-shaped organs, which are slits in the covers 50-160 microns long, leading to a depression on the surface of the body where sensitive cells are located. The lyre-shaped organs are scattered throughout the body.
organs of vision arachnids are simple eyes, the number of which in different species varies from 2 to 12. In spiders, they are located on the cephalothoracic shield in the form of two arcs, and in scorpions, one pair of eyes is located in front and several more pairs are on the sides. Despite a significant number of eyes, arachnids have poor vision. At best, they are able to more or less clearly distinguish objects at a distance of no more than 30 cm, and most species even less (for example, scorpions see only at a distance of a few cm). For some wandering species (for example, jumping spiders), vision is more important, because with its help the spider looks out for prey and distinguishes between individuals of the opposite sex.
Spiders are arthropods that belong to the arachnid class. Representatives of this class, today, there are about 40 thousand species. They differ from each other in the way of life, appearance, type of food. A wide variety of spider species are found in nature: the smallest and harmless spiders (0.37 mm), as well as the most dangerous spiders and even the most poisonous spiders in the world (up to 25 cm). And in this article we will tell you about several amazing and interesting species.
Spider tarantula - Theraphosidae
The tarantula spider is perhaps the largest spider in the world, or rather the family of tarantula spiders (Theraphosidae). Some members of this family can reach 30.5 cm in leg span, such as the king baboon, black and purple tarantula. The body of tarantulas is always densely covered with long and short hairs. The body color can be either gray-brown or bright colors (red, blue, red). Tarantulas live in countries with a hot climate (Africa, South America, Oceania, Australia). These spiders inhabit abandoned bird and rodent nests or burrow near tree trunks. Active mainly in the evening. Then they go hunting or catch a running prey nearby. Tarantulas feed on insects, small birds and rodents. These spiders breed in late summer. The female lays her eggs in a web cocoon, which she carries with her and does not lose sight of. They protect the offspring, so that the spiders that come out of the cocoon sit on the mother's abdomen for some time. But soon they begin to lead an independent life. The poison of the tarantula paralyzes the victim and decomposes its insides, then the spider sucks out the contents of the victim's body. For humans, the poison of the tarantula is not dangerous, but quite painful. The bite site bakes, hurts and swells, sometimes turns yellow. But these symptoms go away after a few weeks.
Spider spider - Araneus
Crosses are members of the Orb Weaver family (Araneidae). They belong to the contract reticulum spiders. They have an egg-shaped convex abdomen, on which there is a pattern in the form of a cross. Body color from gray to red. They are covered with long setae, sparsely located along the body and densely covered with short, fine hairs. The length of the body in the male is 10-11 mm, in the female - 17-40 mm. About 30 species of crosses live on the territory of the CIS and Russia. These spiders are active in the evening. They deftly weave a web, where many small insects come across. Mating and oviposition occurs in autumn. The female lays her eggs in a web cocoon and hides it under the bark or other secluded place. In the spring, spiderlings emerge from the cocoon. By the end of summer, a new generation of spiders grows up, and their mother dies. The cross spider is poisonous, but it is not dangerous for humans. His bite is painful, but the burning and swelling at the bite site disappears after a few hours.
Karakurt spider - Latrodectus tredecimguttatus
This is not a big black spider at all. The body of the female (10-20 mm) is completely black, from which she is also called the black widow, the body of the male (4-7 mm) is also black, but with bright red spots on the abdomen (usually 13 spots ). The karakurt spider lives in Central Asia, Iran, Afghanistan, on the shores of the Mediterranean Sea, in North Africa, Southern Europe, Kazakhstan, in southern Russia and Ukraine. They prefer the slopes of ravines, virgin sagebrush, wastelands, banks of ditches. Karakurts populate abandoned rodent burrows and ventilation systems, braiding the entrance with cobwebs. In such dens, females and males mate in late summer. The female lays her eggs in a cocoon of cobwebs and hangs it in her lair. In spring, spiderlings emerge from cocoons. Karakurt feed on small insects. Their venom is toxic to large animals and humans. There is burning and swelling at the site of the bite. After 10-15 minutes, the poison spreads throughout the body and the person experiences pain in the chest and abdomen. Dizziness, nausea, sweating, palpitations, delirium also occur. And if you do not provide medical assistance in time, a fatal outcome is possible (in most cases). Karakurt bites the skin only by 0.5 mm, therefore it is recommended to burn the bite with a lit match within 2 minutes after the bite.
White karakurt - Latrodectus pallidus
Image of white karakurt
This is a white spider, with long legs and a round abdomen. The abdomen is white or milky, with 4 depressions. Legs and cephalothorax yellow or light brown. The white spider has a body 10-20 mm long. Females are larger than males. White spiders weave a web in the form of a cone, which is connected to a trapping net. They live in North Africa, the Middle East, Iran, Kazakhstan, Turkmenistan and Azerbaijan. The white karakurt spider is not aggressive, but its venom is toxic and can cause complications. Children and the elderly are most affected by the poison. Toxicological studies have shown that the venom of the white karakurt resembles the venom of the karakurt (Latrodectus tredecimtugattus). If you are bitten by this spider, you should consult a doctor.
Camel spider - Camel spider
The camel spider has many names: phalanxes, bihorks, salpugs, hairdressers, barbers, wind scorpion. Body (5-7 cm) slightly oblong, light and dark red, densely covered with long, fine hairs. The body shape of a camel spider is similar to a scorpion, especially with its chelicerae (pincers). With them, he is able to bite through a human nail and even small bones of birds. Also, with his chelicerae, he cuts hairs and feathers from his victims and puts them in his dwelling. The camel spider lives in the desert regions of Asia, Africa, America, and Europe. Phalanx spider nocturnal predator. It is practically omnivorous and carnivorous, feeding on various insects, rodents, lizards. The eyes of camel spiders are like those of scorpions: 2 compound eyes in the middle and one each on the sides of the cephalothorax. Compound eyes are highly responsive to movement, so these spiders are incredibly fast, up to 53 cm/s (1.9 km/h).
The camel spider is not venomous, but it has an incredibly painful bite. And also on its chelicerae, the remnants of the tissues of the previous victim can rot, which can cause serious inflammation.
Jumping spiders - Salticidae
Jumping spiders or jumping spiders are a family of araneomorphic spiders, which includes 610 genera and 5800 species. They live in tropical forests, deserts, semi-deserts, temperate forests and mountains. These are small spiders, up to 2 cm long. The body is pubescent. These spiders have well developed eyesight. They have 8 eyes, thanks to which they see 360º degrees. Jumping spiders differ among themselves in body shape, color and range. There are such types of jumping spiders:
- the golden horse spider lives in the southeast of Asian countries, and is characterized by a long abdominal part and a large first pair of legs. The body has a very peculiar golden coloration. The length of the male rarely exceeds 76 mm, and the females are larger;
- Himalayan jumping spiders are the smallest spiders. They live high above sea level, in the Himalayas, where their only prey is random small insects that are blown onto the mountain slopes by a strong wind;
- the green horse spider lives in New Guinea, New South Wales and Queensland. Often found in Western Australia. The male has a very bright color, and his body is decorated with long "whiskers" of white color;
- a red-backed species of a horse spider to settle in relatively dry areas. The red spider is often found on coastal dunes or oak woodlands in North America. These red spiders are unique in that they are able to build tubular-type silk nests under rocks and on the surface of vines;
- the Hyllus Diardi species has a body up to 1.3 cm long. Compared to other species of horse spiders, it does not weave a web, therefore, to catch prey, it attaches a silk thread to some support, and then jumps from such a kind of "bungee" to its own sacrifice;
- the ant jumping spider looks very similar to an ant and is most often found in tropical zones from Africa to central Australia. Body color can vary from light yellow to black.
Jumping spiders are unique in that they can jump long distances (20 times their body size). Before jumping, they cling to the substrate with a web (thus securing their jump), then push their body out with their hind legs. Jumping spiders are absolutely harmless to humans. They have poison, but it does not affect humans, and their bite is almost painless.
Argiope Bruennichi or spider wasp - Argiope bruennichi
Argiope has a second name spider wasp, as the color of the body and the shape of the abdomen resembles a wasp. Body length 2-3 cm (leg span). The abdomen is elongated with bright stripes, the colors yellow, white, black predominate. The legs are long, thin, mostly in an X-shaped position. The wasp spider lives in Kazakhstan, Asia Minor, Central Asia, China, Korea, India and Japan, North Africa, South and Central Europe, in the Crimea, in the Caucasus. These spiders are also quite common in Russia. Argiope belongs to the family of orb-weaving spiders (Araneidae). It is typical for these spiders to weave a wheel-shaped web, and to have a stabilimentum (zigzag pattern) in the center. This is a forest spider. He very often settles on lawns, forests, gardens, in tall grass, between tree branches. The wasp spider feeds on various insects. Mating occurs after the female molts, while the integument of her body remains soft. The female lays her eggs in a large cocoon (outwardly resembling a seed box of plants) and places it next to the trapping web. Spiderlings emerge from the cocoon at the beginning of autumn and settle downwind on cobwebs. For humans, the wasp spider is not dangerous. Its venom may cause only slight redness, swelling and pain, but these symptoms pass very quickly.
Wolf spiders - Lycosidae
Wolf spiders are a family of araneomorphic spiders with 2367 species. The body color is usually gray-brown. The body is covered with small short hairs. Some species reach more than 3 cm (legspan). The wolf spider lives almost everywhere except Antarctica. He prefers moist forests, meadows, hiding under fallen leaves, stones, wood. They don't spin webs. These are earthen spiders, so they live in a hole, which is only covered with cobwebs inside. If this is a private sector, you can easily stumble upon it in the basement. If there is a garden nearby, it can easily get into your cellar. Active at night. The wolf spider preys on insects or catches those who run near its hole. This spider is a good jumper. He can jump on the victim, insuring himself with a cobweb. Mating takes place in summer. After mating, the female lays her eggs in a cocoon that she wears at the end of her abdomen. After 2-3 weeks, the spiderlings emerge from the cocoon and climb onto the abdomen of the mother's mother. So they sit until they learn to get their own food. The wolf spider is not dangerous to humans. Its sting is equivalent to a bee sting, which causes itching, swelling and redness, which quickly pass.
Harvest spiders - Pholcidae
This family contains about 1000 species of spiders. Harvest spiders have a small body and long thin legs. Body size 2-10 mm. Leg length reaches 50 mm. Body color grayish or reddish. Harvest spiders are ubiquitous. Some species live in people's homes. There they find warm and dry places, mostly near windows. They feed on small insects. These spiders weave a large web in a chaotic manner. The web is not sticky, but when the victim tries to get out of it, it becomes even more tangled. After mating, the females lay their eggs in a web cocoon, which they attach to the side of the trapping nets. For humans, spiders are absolutely harmless. Their venom is harmless and the bite cannot be felt.
Goliath tarantula - Theraphosa blondi
This giant spider is considered the largest in the world. The span of his legs reaches 30 cm. In Venezuela (1965), one of the representatives of this species was listed in the Guinness Book of Records. Its leg span was 28 cm. It is believed that the leg span of Heteropoda maxima is even longer, up to 35 cm. But this species has a small body and long thin legs. So he is small against the backdrop of a massive goliath.
The body of the goliath is light or dark brown in color, densely covered with short hairs. They live in burrows, the entrance of which is covered with cobwebs. This huge spider lives in the tropical forests of Suriname, Guyana, Venezuela, northern Brazil. It feeds on various insects, rodents, frogs, lizards and even snakes. The life expectancy of females is 15-25 years, males - 3-6. These spiders are amazing in that they are able to make a hissing sound by rubbing their chelicerae; the ability to shake off the hairs from the abdomen in the face of the enemy, which cause swelling of the mucosa. Also, the goliath tarantula has large and sharp chelicerae (pincers), with which it can bite very painfully. Their poison is not dangerous for humans, the symptoms are the same as after a bee sting.
Runner Spider (Spider Soldier, Banana, Wandering Spider) – Phoneutria
The Brazilian runner spider is the most venomous spider in the world. The length of its body reaches 15 cm. The body is pubescent, gray-brown in color. It lives in Central and South America. The runner spider feeds on insects, frogs, lizards, small birds. Lives in burrows, under leafy litter. But very often secluded places in people's houses become his dwelling. It is often called banana due to the fact that it is often found in banana boxes. These scary spiders have an incredibly toxic venom that causes instant death, which is why they are the most poisonous spiders in the world. Their venom contains the neurotoxin PhTx3, which paralyzes all the muscles in the human body, causes suffocation, and then death. Only 2-6 hours pass between bite and death. Old people and children are most affected by the venom of the runner spider. To date, there is a vaccine that neutralizes the effect of the poison, therefore, in the event of a bite by a runner spider, it is urgent to consult a doctor.
As you can see, representatives of arachnids are so different: some of them are pleasing to the eye, and at the sight of others, blood freezes in the veins, some can be picked up or taken at home as a pet, and some sow fear and bring instant death. Now you know which types of spiders are absolutely harmless, and which ones you need to stay away from. The good news is that dangerous species of spiders are not found in our area, but mainly in tropical countries. But you never know what can happen... Nature is absolutely unpredictable.
Spider-cross. Structure. Tarantulas. Karakurt
Spiders are the largest order of arachnids in terms of the number of species. The body is subdivided into a fused cephalothorax and a fused abdomen. The cephalothorax is connected to the abdomen by a constriction formed by the seventh segment of the cephalothorax. Chelicerae - hook-shaped, with ducts of poisonous glands. Pedipalps are short. Most often, eight simple eyes are located on the cephalothorax. The respiratory organs of most spiders are represented by one pair of lungs and one pair of tracheae, in some tropical species - only lungs. On the underside of the abdomen are arachnoid warts. From the web, spiders build their shelters, trapping nets, egg cocoons, spermatophore shells, etc. Spiders are characterized by complex behavior.
rice. one.
1 - female, 2 - male.
The female is larger than the male, 20-25 mm long, it has a large rounded abdomen with a characteristic pattern in the form of a light cross on a dark background. Male body length 10-11 mm (Fig. 1).
Eight simple ocelli are arranged in two rows on the anterior part of the cephalothorax. There are six pairs of limbs on the cephalothorax: chelicerae, pedipalps and four pairs of walking legs. Chelicerae consist of two segments, the terminal segments look like curved claws. At the base of the chelicerae are poisonous glands, the ducts of which open at the tips of the claws. With chelicerae, spiders pierce the covers of victims and inject poison into the wound. Pedipalps have the appearance of segmented limbs. In males, on the terminal segment of the pedipalps, there is a copulatory apparatus with a reservoir, which the male fills with seminal fluid. During copulation, the male injects the pedipalps, along with seminal fluid, into the female's seminal receptacle. Walking legs are seven-membered.
In the abdominal cavity there are arachnoid glands that produce various types of cobwebs.
rice. 2.
1 - simple eyes, 2 - poisonous gland, 3 - chelicerae, 4 - brain,
5 - mouth, 6 - subpharyngeal ganglion, 7 - blind outgrowths
midgut, 8 - lung sac, 9 - ovaries, 10 - arachnoid
glands, 11 - spider warts, 12 - anus,
13 - Malpighian vessels, 14 - glandular protrusions of the middle
intestines (liver), 15 - heart, 16 - sucking stomach.
To catch prey, the cross weaves a net from a web in the crown of trees. The prey are flying insects. The body of the victim caught in the net is pierced by spiders with chelicerae, poison and digestive enzymes of the salivary glands and liver are injected inside. Pedipalps serve to hold prey. Under the action of enzymes, the tissues of the prey are digested, the spider sucks in the semi-digested food, and only covers remain from the victim.
The anterior intestine, lined with cuticle, consists of a strongly muscled pharynx, esophagus, and sucking stomach. The ducts of the salivary glands open into the pharynx. The middle intestine in the cephalothoracic region has 5 pairs of long blind lateral protrusions, which allow spiders to absorb a large amount of food. In the abdominal region, the middle intestine forms paired glandular protrusions - the liver. It not only secretes digestive enzymes, but also serves as a site for intracellular digestion (liver cells are capable of phagocytosis). The terminal section of the midgut forms a swelling into which the channels of the Malpighian vessels flow. Thus, extraintestinal, intestinal and intracellular digestion takes place in spiders.
The circulatory system is open, the heart is located on the upper side of the abdomen, has 3 pairs of ostia. The anterior aorta arises from the anterior end of the heart. The terminal branches of the arteries pour hemolymph into the system of lacunae, from where it enters the abdominal sinus, washing the lung sacs, from there to the pericardial part of the body cavity, and then through the ostia to the heart.
The respiratory organs are represented by a pair of lung sacs, forming leaf-like folds, and two bundles of tracheae. The respiratory openings of the trachea open on the underside of the abdomen.
Excretory organs - Malpighian vessels. The main excretory product of arachnids - guanine - is removed from the body in the form of crystals.
Due to the fusion of the segments, the ganglia converge. The brain is formed by the merged ganglia of the head and chest, the abdominal nerve chain is represented by a large knot in the abdomen.
Vision is poor, hearing organs are poorly developed, represented by auditory vesicles. The organs of seismic sense, balance (statocysts) and touch are well developed.
In autumn, the female spins a cocoon from a special web, in which she lays several hundred eggs. The cocoon hides in cracks in the bark. After the breeding season, females and males die. Eggs overwinter, young spiders emerge from them in spring.
rice. 3.
Tarantulas (Lycosa sp.)(Fig. 3) - large (3-4 cm) spiders living in vertical burrows, the walls of which are braided with cobwebs. The entrance to the mink can be tightly closed with a lid woven from the web. During the day, tarantulas hide in these burrows and hunt at night. For the winter, the hole deepens, the entrance to it is clogged with earth. Eggs are laid in early summer.
rice. 4. Karakurt (Latrodectus
tredecimguttatus)
Tarantula venom is not dangerous for humans; in the worst case, a slight inflammation occurs at the bite site.
(Fig. 4) lives in the Crimea, the Caucasus, Kazakhstan, etc. It poses a great danger to humans, cattle, horses and other animals. Sheep are immune to the poison of karakurt. Karakurts are small black spiders with red dots on their abdomen. The body length of the female is up to 20 mm, the male is up to 7 mm. Favorite habitats are wastelands, slopes of ravines, virgin sagebrush. In the recesses of the soil, often in the burrows of rodents, the female arranges lairs. Trapping threads are stretched at the entrance to the lair. The eggs overwinter in cocoons.
The most poisonous are sexually mature females, their poison is 15 times stronger than the poison of a rattlesnake. The bite of such a female causes severe pain, severe poisoning and can be fatal.
Description of other classes and orders of the phylum Arthropoda:
- Class Arachnids
- Order Spiders (Aranei)
To class Arachnids include mainly terrestrial species (more than 60 thousand species).
These include scorpions, harvestmen, ticks, spiders and other members of the class.
Among ticks and spiders, there are secondary forms (for example, the silver spider).
External structure
In arachnids, the body is divided into two departments - cephalothorax and abdomen, no antennae.
Located on the cephalothorax four pairs of walking limbs and two pairs of modified limbs (mouth organs - chelicerae and leg tentacles), serving to capture and grind food.
Hook-shaped chelicerae The spider grabs its prey. Inside the chelicerae there is a channel through which digestive juice enters the body of the victim from the poisonous glands located at the base of the chelicerae. Next to the chelicerae are short organs of touch covered with sensitive hairs - leg tentacles.
At the lower end of the abdomen are three pairs of spider warts that produce webs are modified abdominal limbs.
The liquid released from the spider webs instantly hardens in the air and turns into a strong spider web.
Different parts of spider warts secrete different types of webs. Spider threads vary in thickness, strength, stickiness. The spider uses various types of cobwebs to build a trapping web: at its base, the threads are more durable and non-sticky, and the concentric threads are thinner and stickier. Spiders use the web to strengthen the walls of their shelters and to make cocoons for their eggs. Young spiders use long web threads to move in space, which contributes to their settlement. With the help of web threads, spiders can descend from tree branches and other supports to the ground and rise.
In ponds and rivers with slow-flowing water lives a silver water spider, which builds its nest in the water from the web and fills it with air.
Eyes in arachnids simple.
The relatively weak development of the organs of vision is compensated by the well-developed organs of touch, which play a leading role in the orientation of arachnids in the environment. They also have organs that respond to chemical stimuli, as well as organs of smell and taste.
Internal structure
bodies breathingin spiders are lungs (lung sacs) and trachea.
Scorpions- only lungs.
Ticks gas exchange takes place through the skin no special respiratory organs.
The circulatory system is open. The blood is colorless.
Digestive system The spider consists of a mouth, pharynx, esophagus, stomach, intestine and anus.
arachnids - predators. To attack other animals, they have various devices: from poisonous glands to spider web warts for making trapping nets. Spiders inject digestive juice into the body of the victim, which dissolves its tissues. This is how it goes extraintestinal digestion. The spider then sucks (using sucking stomach) liquefied food. Long blind outgrowths in the midgut increase its volume and absorption surface. The remains of undigested food are excreted through anus.
Nervous system consists of a well developed supraesophageal node and abdominal chain. Arachnids have developed complex instinctive behavior.
arachnids - dioecious animals. Fertilization in representatives of some species external, other's - internal. Meets them parthenogenesis - reproduction without fertilization when the female lays unfertilized eggs, from which only females develop.
Usually arachnids lay eggs, but there are also viviparous ones.
Development without transformation, small individuals similar to adults emerge from the eggs. In many species, care for offspring is observed: females guard the cocoon with eggs.
Distribution and significance
scorpions live in countries with a warm or hot climate, sometimes found in the mountains. Scorpions hunt at night. By secreting venom, scorpions immobilize prey or kill it. They feed on various arachnids, lizards or mouse-like rodents. Scorpions can be dangerous to humans.