Who coined the term genetics. Genetics as a biological science

class arachnids, unlike crustaceans, live mainly on land, breathe with the help of trachea and lungs. The class includes three orders, on the representatives of which one can trace the process of fusion of body parts. So, in a detachment of spiders, the body is divided into a cephalothorax and abdomen, in scorpions it consists of a cephalothorax, anterior abdomen and posterior abdomen, in ticks all sections are merged into one shield.

Common signs of arachnids: lack of antennae, four pairs of walking legs, tracheal or pulmonary respiration, permanent perioral appendages - upper tentacles and leg tentacles. On the cephalothorax are four pairs of simple eyes, mouth organs and limbs (walking legs). The most common are spiders and mites.

Spider Squad

A typical representative of the order of spiders is cross spider. It can be found in forests, parks, on estates, in houses where they weave large trapping nets from cobwebs. In a spider, the first pair of oral organs are the upper jaws, equipped with sharp, downward-curved claws.

At the end of the claws, the excretory ducts of the poisonous glands open. The jaws serve the spider for killing prey and for protection. The second pair of mouth organs are the leg tentacles, with which the spider feels and turns the victim while eating.

Four pairs of jointed walking legs are covered with sensitive hairs. The abdomen of arachnids is larger than the cephalothorax. At the posterior end of the abdomen, spiders have arachnoid warts, into which the arachnoid glands open. The substance secreted by the glands hardens in air, forming arachnoid threads. Some glands secrete a strong and non-adhesive cobweb, which goes to form the skeleton of a trapping network. Other glands secrete small sticky threads with which the spider builds a trapping web. Third glands secrete a soft silky web used by the female to weave a cocoon.

The spider that has fallen into the trapping net entangles the victim with a sticky web, sticks the claws of the upper jaws into the prey and injects into it a poisonous liquid that dissolves soft tissues and acts as digestive juice. Leaving the victim wrapped in a web, the spider steps aside, waiting for its contents to be digested. After a while, the spider sucks in partially digested food. So in spiders, partial digestion of food occurs outside the body.

The respiratory organs of the spider are represented by lung sacs that communicate with the environment. In addition to them, the spider has tracheae in its abdomen - two bundles of respiratory tubes that open outwards with a common respiratory opening.

The circulatory system of a spider is basically the same as that of a cancer.

The role of the excretory organs is performed by the Malpighian vessels, the spider has one pair of them, but they branch. The hemolymph (blood mixed with lymph) of the spider washes these vessels and the metabolic products exit through the gaps, then enter the intestines and are then excreted.

The nervous system is formed by the subpharyngeal ganglion, the brain, from which the nerves extend to various organs.

Spiders have numerous and varied sense organs: organs of touch (hairs on the body of the spider and on the tentacles), smell and taste (on the tentacles and walking legs), taste organs are also present on the lateral parts of the pharynx; organs of vision (eight simple eyes). Some spiders are able to distinguish color, especially those. which are looking for prey on the flowers of plants (crab spiders).

Spiders are dioecious animals. Females are larger than males. In autumn, the female spins a cocoon of cobwebs and lays her eggs in it. In it, eggs hibernate, and in spring spiders hatch from them. Most spiders are beneficial: many small mammals, birds, lizards, and some insects feed on them. Among the spiders there are also poisonous ones - tarantula and karakurt. They are very dangerous for humans and pets.

Squad of pincers

In most representatives of the order of ticks, the body does not have a clear division into segments or sections. There are a lot of ticks. Some of them live in the soil, others - in plants, animals and humans.

Unlike spiders, flares have an indirect development. A six-legged larva emerges from the egg, in which, after the first molt, a fourth pair of legs appears. After several molts, the larva turns into an adult.

Red spider mite settles on the leaves of cotton and other valuable plants. It reduces cotton yields and causes plant death.

flour mite settles in onions and grains. Eating the germ of the future plant in the grain, it causes the death of the seeds. It causes food spoilage in warehouses. for example, various cereals, bread products, sunflower seeds. Cleanliness and ventilation of the premises where food is stored is one of the main measures to combat flour mites.

scabies mite (scabies itch) causes diseases such as scabies in humans. Females of this type of mites are introduced into the more delicate areas of human skin and gnaw their moves in it. Here they lay their eggs. Young flares come out of them, again gnawing passages in the skin. Keeping your hands clean prevents this dangerous disease.

Scorpion Squad

Scorpions live in countries with warm and hot climates, and are found in a wide variety of habitats: from humid forests and sea coasts to barren rocky areas and sandy deserts. Often scorpions settle in human dwellings.

Scorpions are mostly viviparous, some species lay eggs in which the embryos are already developed, so that juveniles soon hatch. This phenomenon is called ovoviviparous. A scorpion becomes an adult a year and a half after birth, making 7 molts during this time.

A scorpion sting is a means of attack and defense. On small invertebrates, which usually serve as food for a scorpion, the poison acts almost instantly: the animal immediately stops moving. For small mammals, scorpion venom is mostly fatal. For a person, a scorpion sting is usually not fatal, but a number of cases are known with very serious consequences and even death.

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Introduction

Spiders (Aranei)

The name of the class Arachnoidea comes from the Greek. arachne - spider. In ancient Greek mythology, Arachne was the name of a girl who was such a skilled weaver that, having challenged the very patroness of this craft, the goddess Athena, to a competition, she wove a fabric better than she. Annoyed, the goddess turned her rival into a spider, announcing that from now on Arachne and her entire family would spin and weave until the end of time.

Spiders are the largest order of arachnids. Today, scientists have described about 35 thousand species of spiders, and this number is believed to increase to 50 thousand. Spiders are currently one of the most prosperous groups of animals. It is difficult to find a place in nature where spiders would not live. They have mastered all the natural zones of the Earth - from deserts and tropical forests to Antarctica. The conquerors of Everest found one of the species of spiders at an altitude of 7 kilometers! In the taiga, there can be up to 300-350 specimens of small spiders per square meter of soil.

The complexity and expediency of the behavior of spiders has attracted the attention of scientists since ancient times. Aristotle made observations of their life and customs. Nowadays, spiders are being studied in various directions by scientists from many countries of the world. The branch of knowledge about spiders is called araniology. The literature on spiders is vast, with thousands of specialized and popular works. But there are few general reports, and almost all of them are foreign. Such are the sections on spiders in the multi-volume manuals on zoology compiled by the French araneologist Millo (1949) and the German zoologist Kestner (1955, 1959), the English works on the biology of spiders Bristow (1939, 1941), Savory (1961) and others.

1. General characteristics

Detachment - spiders (Aranei) Spiders are the largest detachment of arachnids. More than 30,000 species have been described, and experts believe that this figure will increase significantly in the future, since the world's spider fauna has been studied very unevenly and incompletely. All land is inhabited by spiders. Like insects and mites, they live everywhere, and there is literally no corner in nature where there would not be certain types of spiders. In order to move on to a more detailed consideration of spiders, let's try to immediately understand the nature of this huge detachment and the features of its diversity. In all the main life manifestations that support the existence of the species - obtaining food, reproduction, resettlement and experiencing adverse conditions - spiders use the web. A shelter and a dexterous device are made from it, with its help a complex mating procedure takes place, a facial cocoon and a wintering bag are woven from it, juveniles are carried by the wind on it, etc. The spider interacts with the outside world not so much directly, like other animals, but through its arachnoid adaptations, which for each species correspond to its vital needs and the specific environment in which it lives. In other words, the relationship with the environment is carried out in spiders through arachnoid activity, which, like all spider behavior, is based on instincts. A comparative study of spiders shows that the evolution of arachnoid activity, the evolution of instincts, is the leading direction in the evolutionary development of spiders, in which this peculiar detachment reached an unprecedented flowering. A clear confirmation is the nature of the diversity of spiders.

arachnid biological arachnoidea

2. Systematic position

A detachment of the arachnid class also includes ticks, scorpions, haymakers.

Three suborders: lyphistiomorphic, or arthropod, spiders (Liphistiomorphae), mygalomorphic, or tarantula spiders in the broad sense (Mygalomorphae), and higher araneomorphic spiders (Araneomorphae). The former division of spiders into four-lung (Tetrapneumones) and two-lung (Dipneumones) spiders is less natural.

3. Distinctive features

So, the signs by which a spider can be unmistakably distinguished are: a sharp separation of the cephalothorax and abdomen, chelicerae with a claw-like terminal segment, small tentacle-shaped pedipalps, and arachnoid warts on the abdomen. The body shape of most spiders is fairly uniform. The cephalothorax, as a rule, is smaller than the abdomen, narrowed and blunted in front, the abdomen is ovoid. Deviations are numerous, found in different families. There are spiders that are very elongated, with long thin legs, which they stretch along the body, becoming invisible among the narrow leaves of cereals and sedges where they live. In others, living under the bark, on tree trunks, on flowers, the body is flattened, the abdomen is often expanded. A number of tropical spiders have long spikes and bizarre outgrowths on their abdomens. Sometimes the shape of the cephalothorax changes, for example, the eyes are raised on a long outgrowth, etc. The sizes vary widely. The smallest spiders are 0.8 mm, the largest tropical tarantulas are up to 11 cm in length, and with legs up to 20 cm. Our large tarantulas reach 3.5 cm, and in females of one Far Eastern species of crosses, the abdomen is the size of a walnut . The coloration is very diverse, especially in tropical spiders. Along with dark and nondescript forms, there are many brightly colored, one-color or with complex patterns. Often yellow in combination with white. There are bright red forms or black with a red belly. Many species living among plants are colored in various shades of green, sometimes in combination with yellow, brown and other tones. There are species with gold and silver spots, metallic shiny, mother-of-pearl. The cephalothorax of spiders is covered with a solid solid shield, in front of which there are eyes, usually four pairs. Chelicera short, 2-segmented. Their claw-shaped or crescent-shaped end segment, bending, enters the groove on the main segment like the blade of a penknife. At its end, the duct of the poisonous gland opens. In lyphistio- and mygalomorphic spiders, the chelicerae are located horizontally, and the terminal segments are bent downwards; in higher araneomorphic spiders, the main segments are directed downward, and the terminal segments are directed inward, towards each other. With chelicerae, the spider seizes and kills prey, kneads and tears it, defends itself from enemies, cuts the threads of the web, drags egg cocoons, in some cases the male holds the female with chelicerae during mating, mink species dig the ground with chelicerae, etc. Pedipalps look like legs, but shorter and with one claw. Their coxae are usually equipped with lobes that limit the preoral cavity and are covered with hairs that serve to strain liquid food. The tentacles of the pedipalps serve as organs of touch and, as a rule, do not participate in locomotion. In sexually mature males, the pedipalps are modified in connection with their copulatory function, their terminal segments are turned into copulatory organs, usually very complex. The legs are 7-segmented, their coxae are attached around a solid pectoral shield. The tarsi have two sickle-shaped, usually comb-like claws. Between them is an unpaired appendage (empodium), also claw-like, or in the form of a sticky pad. Spiders that make webs also have additional claws formed by bristles, often serrated. The legs are covered with hairs, partly simple, adjoining, partly protruding, different in shape and size. The relative size of the legs varies greatly depending on lifestyle. Sometimes individual pairs of legs differ from the rest, such as the prehensile forelegs of some jumping spiders. The functions of the legs are varied, in addition to movement, they can serve to dig holes, hold prey, an egg cocoon, etc. Various web devices are woven with the help of the legs. With its feet, the spider pulls and breaks the cobweb threads, measures the distance between the radii and turns of the spiral of the snare, combs the web, etc. The legs are richly equipped with sensory organs, tactile and olfactory. The abdomen of the vast majority of spiders is non-segmented, its segments are fused. The integuments of the abdomen are elastic, usually densely pubescent with hairs. Only in rare cases, secondary sclerites form on the abdomen. In primitive lyphistiomorphic spiders, unlike all the others, the dissection of the abdomen is well expressed, all its segments have tergites, and on the ventral side they are separated by transverse grooves. Traces of segmentation of the abdomen are preserved in higher spiders in the structure of the musculature, sometimes in the pattern of the abdomen. The segments are well expressed in the embryo; in young spiders, the yolk mass that fills the intestines is also segmented. Judging by all these data, 11 segments are combined in the composition of the abdomen of spiders, and the tergal sections are more fully developed than the sternal ones, and several posterior segments atrophy to one degree or another. The genital opening opens on the abdomen, the respiratory organs are located - the lungs and trachea - and spider warts. As mentioned, spider warts are modified abdominal legs. They are located on the abdomen from below in front of the tubercle with the anus. At the ends of the warts there are numerous chitinous arachnoid tubes (modified hairs), which open the ducts of the arachnoid glands. Lyphistiomorphic spiders of arachnoid warts have four pairs: two pairs of external ones, developing from the rudiments of the limbs, and two pairs of internal ones, formed as outgrowths of the body wall. The warts here are multisegmented, which resembles real legs. Most spiders retain three pairs of warts: two pairs of outer warts, usually 2-segmented, and a pair of posterior median, non-segmented. In a number of families and genera of spiders, a further reduction in the number of warts to two and even to one pair is observed, but spiders that are completely devoid of spider warts are unknown. The anterior medial pair of warts in the spiders of the Cribellatae group is turned into the so-called cribellum - a small plate pierced by pores through which the substance of special arachnoid glands is secreted. In some spiders, individual pairs of warts are elongated, sometimes even longer than the body. The spider glands are located in the abdominal cavity, in most cases they are well developed and numerous. The duct of each gland opens at the end of the arachnoid tube. Along with the usual tubules, there are a small number of so-called spider cones, on which the ducts of larger glands open. Relatively primitive forms of arachnoid glands are characteristic of lyphistio- and mygalomorphic spiders, which have bundles of small oval glands, but already here their number can reach several hundred. Araneomorph spiders possess several types of spider glands, producing different varieties of webs. The arachnoid apparatus is most complex in cross-spiders (family Araneidae), in which up to six types of arachnoid glands are distinguished, and on arachnoid warts there are a total of more than 500 tubes and about 20 arachnoid cones. The web secreted by the glands of different types is used for various purposes. So, for building a trapping network, the cross uses the secret of all its glands, except for the so-called tubular, the web of which goes to the facial cocoons. The web frame and the radii stretched inside are made from relatively thick dry threads secreted by the ampulloidal glands. At the same time, several glands act simultaneously and individual thin threads are connected by a liquid secret into a thicker “cable”. The so-called pear-shaped glands secrete bundles of thin fibers, with which the ends of the main threads are attached to surrounding objects. The spiral thread is made from the web of the lobular glands and is covered with a sticky secretion of the arborescent glands, which does not harden in the air and soon collects in microscopic droplets. Thanks to this, the trapping nets remain sticky for a more or less long time. The spiders of the Cribellatae group retain their adhesiveness for a particularly long time. On the sieve cribellar plate, ducts of many (up to 600) special arachnoid glands open. The secreted web is vigorously combed with the hind legs, on the penultimate segment of which the cribellate spiders have rows of strong bristles for this (the so-called calamistrum). It turns out a special kind of "yarn": the axial threads are surrounded by a mucous sleeve, inside which there is a thread bent by numerous loops. From such a mucous web, cribellate spiders build trapping webs of various shapes, very sticky and long-lasting. The web is close in chemical composition to silkworm silk, from which it differs in a low content of a gluing substance - sericin, which is soluble in water. The basis of spider silk is the fibroin protein formed by a complex complex of albumins, b-alanine and glutamic acid. In terms of physical properties, the web is also close to caterpillar silk, but much more elastic and durable. The breaking load for the web is from 40 to 261 kg per 1 mm² of the thread section (in some Araneus), while for caterpillar silk it is only 33-43 kg per 1 mm². On the ventral side of the abdomen, closer to the base, spiracles open. The respiratory apparatus of spiders is interesting in that in this detachment there is a change of lungs by tracheas. Primitive spiders have two pairs of lungs. Such are the lyphistio- and mygalomorph spiders (four-lungs of the former classification) and the small family Hypochilidae among the araneomorph spiders. In the vast majority of the latter (two-lungs of the former classification), tracheae develop in place of the posterior pair of lungs, and in several families (Caponiidae and others), tracheae also form in place of the anterior pair of lungs. Thus, among spiders there are four-lungs, breathing only with lungs, two-lungs, breathing with lungs and tracheas, and lungless, breathing only with tracheas. The lungs of spiders are similar in structure to the lungs of other arachnids. The tracheae are distinguished by a variety of structures and in most spiders they are relatively poorly developed. There are tracheas of local and general significance. The former are represented by bundles of short, usually unbranched tubes that do not extend beyond the abdomen. The second ones are longer, sometimes anastomosing and branching, penetrating through the stalk of the abdomen into the cephalothorax and its limbs. Most two-lung spiders have four non-branching tracheal trunks. Further complication of the trachea is manifested in the formation of numerous thin tubes at their ends, and the trunks of the middle pair penetrate into the cephalothorax, for example, in jumping spiders. The tracheae are most differentiated in lungless spiders. Bundles of short thin tracheas depart from the anterior stigmas, which are washed by the blood of a special tracheal sinus, that is, they function as a kind of secondary lungs. Thick trunks extend from the posterior stigmas into the cephalothorax and abdomen, which branch and deliver oxygen directly to organs and tissues, i.e., they function as tracheae should. The cuticular walls of the trachea have supporting rod-shaped thickenings, very similar to the rod apparatus of the lung pockets, which prevents them from collapsing. Less commonly, the tracheae have spiral thickenings, which are so characteristic of the trachea of insects, and among arachnids, salpug and harvestmen. In most spiders with tracheae, pulmonary respiration still predominates. In this regard, the circulatory system is well developed. Covering lung stigmas with petroleum jelly leads to a rapid decrease in heart function and eventually to death. Only in forms with well-developed tracheae, lung exclusion does not cause noticeable disturbances in vital activity. It can be said about spiders in general that they, populating a wide variety of habitats, including dry ones, were not in too much of a "rush" to replace their lungs with tracheae and conveyed to us all the stages of this process. This is seen as a manifestation of the cobweb activity of spiders, thanks to which they everywhere create for themselves a shelter with a suitable microclimate. The central nervous system of spiders is highly concentrated. The sense organs play an important role in their complex life. Prevailing importance, especially in the tenet forms, is the sense of touch. The trunk and appendages are covered with numerous tactile hairs. Hairs of a special structure - trichobothria are found on the pedipalps and legs. There are up to 200 of them. With the help of trichobothria, the spider feels the most insignificant puffs of air, for example, from a flying fly. Trichobothria perceive rhythmic vibrations in a wide range of frequencies, but not directly as a sound, but through the vibration of the web threads, that is, as tactile sensations. If you touch the web of a cross-spider with a sounding tuning fork, the spider will head towards it as if it were prey. However, the sound of the tuning fork not touching the web puts the spider to flight. It is believed that the sound is perceived by some other organs. It is known that spiders often enter the network at the sound of a musical instrument, such as a violin. With such a positive reaction, obviously, there is not an auditory, but a tactile sensation of the resonating threads of the web. Another kind of tactile sense is the perception of the degree of tension of the web threads. When their tension changes in the experiment, the spider seeks its shelter, always moving along the most tense threads. The crosser runs much more quickly towards a heavy object that has fallen into the net than towards a light one.

The organs of balance and hearing are unknown in spiders, but they have these senses. Having mastered the prey, the spider returns to the center of the web. If you place a fly in a net above the center, the spider will move upward towards it. Turning the web 90 or 180° can disorient the spider. Having finished with the fly, he begins to descend the net, as if to its center, and finds himself at the edge of the net. In this case, the feeling of heaviness and balance prevails over the changed tactile sensations. The presence of hearing in spiders is confirmed by a number of facts. The spiderycosides respond to the buzzing of a hidden fly that they cannot see, the araneids raise their front legs at the sound of a certain tone. Some spiders make sounds, and in some cases their role in attracting sexes has been proven. Sound organs are stridulators, i.e. surfaces rubbing against each other with ribs or rows of setae. They occur on chelicerae and pedipalps or only on chelicerae, on contiguous parts of the cephalothorax and abdomen, and in other places. The sound apparatus is either only males, or both sexes. The latter is observed in some mygalomorphic spiders, which have rows of special setae (comb and lyre) on their chelicerae and pedipalps. The spider quickly rubs them against each other. The sounds made by small spiders (family Theridiidae, Linyphiidae, etc.) are very weak and are recorded only by special devices. Their height is 325-425 vibrations per second. Some migalomorphic spiders make sounds audible to humans - crackling, buzzing, hissing. In a number of cases, the sound is combined with a threat posture and apparently has a warning value. The organs of smell are the tarsal organs on the tarsi of the forelegs and the lyre-shaped organs, which are present in large numbers on the trunk and appendages. Spiders distinguish the smells of volatile substances, but usually react at a close distance from the source of the smell. Males distinguish the tenet of a sexually mature female from the tenet of an immature female by smell. The role of smell in this case has been proven experimentally. If an ethereal extract is made from the cobweb or the torn off leg of a sexually mature female and poured into a saucer, then after the evaporation of the ether, the male planted in the saucer exhibits characteristic sexual arousal. The tarsal organs also serve as taste organs, with their help the spider in the experiment distinguishes between pure water and solutions of various substances. Apparently, these organs play a role in finding the drinking water needed by some spiders. Sensitive taste cells are found in the walls of the throat of spiders. In the experiment, spiders well distinguish pieces of elderberry core soaked in a nutrient solution from the same pieces soaked in water. The first are sucked out, and the second are removed from the nets.

The vision of spiders is imperfect, especially in the tenet forms. Stray spiders see better, especially active during the day. The eye is usually four pairs. The front medial eyes, called the main ones, are dark; the rest, secondary eyes, usually shiny due to the inner shell (mirror) reflecting light. The size and mutual position of the eyes are different in different systematic groups of spiders. More often they form two transverse rows, but they are arranged differently. Sometimes individual pairs of eyes are enlarged, for example, the four anterior eyes in jumping spiders, the medial posterior eyes in Dinops (family Dinopidae). In some cases, the number of eyes is reduced to six, four or two. Among the cave spiders there are blind ones. The eyes of web spiders are located so that they cover a large field of view, but they mainly distinguish the strength and direction of light, capturing the movement of large objects. Many spiders sitting on nets notice an approaching person and fall on a web of thread. With a sharp change in the usual lighting of surrounding objects, mink spiders lose their orientation and cannot immediately find their lair. Sidewalk spiders (family Thomisidae), lying in wait for prey on flowers, notice a cabbage butterfly at a distance of 20 cm, and a fly only at a distance of 3 cm. but do not distinguish its form. A kind of exception is represented by small jumping spiders (family Salticidae). Their long-focus main eyes produce a large image on the retina with a small field of view (as in a camera with a telephoto lens). Unlike other eyes, the visual elements of the retina are densely located here, due to which the vision is objective: at a distance of 8 cm, the spider sees the fly in detail. The small field of view of these eyes is compensated by a remarkable feature: they can move with the help of special muscles. The spider follows its prey with its eyes - a rare example among terrestrial arthropods. Side eyes do not distinguish the shape of objects, but are located in such a way that the spider notices any movement in front, behind itself and above itself. The anterior lateral eyes have a total binocular field of view of about 40°, due to which the spider perceives the volume of objects and the distance to them. The eyes of horses act as a single visual apparatus. If a fly approaches the spider from behind, it notices its movement with its rear eyes at a distance of 20-25 cm and turns towards it so that it enters the field of view of the front eyes. Now it is perceived more clearly and in space. Then the spider catches it with its main eyes, perceives it in close-up and begins to follow it with its eyes. At a distance of 8 cm, the object is recognized as prey, from 4 cm the spider begins to creep up and from 1.5 cm jumps at the fly with lightning speed with such accuracy that it rarely misses. Good vision of horses helps them to move in the grass, deftly jumping from leaf to leaf. With the help of the eyes, the male detects the female, and being blinded, does not recognize her and does not perform his characteristic mating dances. Placed in front of a mirror, the male racer reacts to his image as a rival, assumes a pose of threat or rushes at him. Steeds and some other spiders distinguish the color of objects. This was established by several methods, including the development of conditioned reflexes. The spiders were exposed to flies under red and blue, and under red and green light. Red lighting was accompanied by electric shock irritation. After several repetitions of the experiment, the spider took the fly only under blue or green light. The activity of spiders depends on the temperature and humidity of the air, most of them are warm and moisture-loving, but there are many species that are active at relatively low temperatures. During winter thaws, at +6, +7°C, some small spiders sometimes appear en masse on the snow. Spiders, especially web spiders, like many insects, are also sensitive to changes in barometric pressure, due to which they are known as "weather predictors". Indeed, they intensively build a net in good weather, and before bad weather they hide in their shelters and often even stop responding to prey that has fallen into the net.

Spiders are very voracious predators, feeding mainly on insects, which they suck. There are various methods of catching prey. Stray spiders lie in wait for prey, sneak up to it and overtake it with one or more jumps. At the same time, already in vagrant forms, prey is often entangled in cobweb threads. Sedentary spiders almost always make some kind of trapping device from the web, from simple signaling threads stretched from the mouth of the lair in which the spider sits, to very complex trapping nets. The prey is usually killed with poison. Poison glands are very characteristic of spiders. In primitive forms, the glands are small, entirely placed in chelicerae; Araneomorphae are characterized by large glands protruding into the cavity of the cephalothorax. Each of the two glands is surrounded by spiral muscles, during the contraction of which the poison is injected through the hole at the end of the claw-like segment of the chelicerae into the body of the victim. On small insects, the poison acts almost instantly, but larger ones continue to beat in the nets for some time. The prey is entangled in a web, but if it is large and the spider cannot cope with it, it frees the prey itself. Often, insects with a pungent odor - bedbugs, etc. - are thrown out of the nets. Food objects are very diverse. Usually these are a variety of insects that are suitable in size. It is mainly flying forms that fall into the network of web spiders, most often dipterans. A spider sucking a fly is a picture for everyone for granted. The species composition of consumed insects depends on the habitat and season. Many spiders that live near the soil or in burrows feed mainly on beetles and orthoptera. Some, along with insects, are dragged into the mink and eat earthworms and snails. There are spiders that have specialized in choosing prey, hunting only ants or only spiders of other species (family Mimetidae). Water spider Argyroneta hunts for larvae of aquatic insects, crustaceans, fish fry. Huge tropical tarantulas kill and eat small birds on occasion, although they mainly feed on insects. In captivity, tarantulas willingly eat small lizards, frogs, and mice. The Brazilian tarantula Grammostola feeds on young snakes and destroys them in large numbers. Amphibiotic spiders (Dolomedes, etc.), running through the water, catch small fish, tadpoles and insect larvae. According to the method of nutrition, spiders in their most complete form represent the arachnid type. The filtering apparatus of the preoral cavity and pharynx, the narrow esophagus, and the powerful sucking stomach are all adaptations for nourishing liquid food. Having caught and killed the prey, the spider tears and kneads it with chelicerae, while pouring out the digestive juice that dissolves the internal tissues. The escaping liquid is sucked up. The secretion of juice and the absorption of food droplets alternate, the spider turns the victim, processing it from different sides, until a wrinkled skin remains. Spiders that feed on insects with a hard cover, such as beetles, inflict a wound with chelicerae on the articular membrane, more often between the head and chest. Digestive juice enters through this opening and the contents are sucked out. In the digestion and excretion of spiders, the role of a large liver is essential, in the cells of which intracellular digestion of food and absorption take place. Part of the liver cells, overloaded with excretion, goes into the intestinal lumen and mixes in the cloaca with the white secretions of the Malygian vessels. Excrement is thrown out in small drops before a new meal.

The biology of reproduction of spiders in terms of the complexity and originality of the observed phenomena surpasses everything that is characteristic of other arachnids, and this is again due to the use of the web. Sexually mature male spiders in lifestyle and appearance, as a rule, are very different from females, although in some cases males and females are similar. Usually the male is smaller than the female, with relatively longer legs, and sometimes males are dwarfed, 1000-1500 times smaller in volume than females. In addition to size, sexual dimorphism often manifests itself in certain secondary sexual characters: in the bright pattern of males, in the special form of separate pairs of legs, etc. Males, as a rule, are less common than females, and in some species they were not found at all. At the same time, the virgin development of eggs in spiders seems to be the rarest exception. In web spiders, mature males usually no longer build trapping webs, but roam in search of females and are caught on the female's webs during a short mating period. The internal organs of the reproductive system of spiders generally have a fairly common structure. The testicles are paired, the convoluted seminal ducts are connected near the genital opening, which in the male has the appearance of a small gap. The ovaries are paired, in some cases fused at the ends into a ring. Paired oviducts are connected to an unpaired organ - the uterus, which opens with an oviduct. The latter is covered by a folded elevation - the epigyne. There are seminal sacs - sacs from which the tubules depart to the excretory part of the genital tract and to the epigyne, where they usually open independently of the oviduct. Aggregate organs are formed on the pedipalps of the male only during the last molt. Before mating, the male releases a drop of sperm from the genital opening onto a specially woven spider web, fills the copulatory organs of the pedipalps with sperm, and when mating, with their help, injects the sperm into the female's seminal receptacles. In the simplest case, the pedipalp tarsus has a pear-shaped appendage - a bulb with a spiral spermatic canal inside. The appendage is extended into a thin nose - an embolus, at the end of which a canal opens. During mating, the embolus is inserted into the tubule of the female's seminal receptacle. In most cases, the copulatory organs are more complex, and the ways of their complication can be traced within the order and are somewhat different in different groups of spiders. The tarsi of the pedipalps are usually enlarged. The articular membrane of the bulbus turns into a blood receptacle, which at the time of mating bubble-like swells under the pressure of the hemolymph. The spermatic duct forms complex loops and opens at the end of a long embolus, flagellate or otherwise. Often there are additional appendages that serve to attach during mating. The structure of copulatory organs in detail is very diverse, characteristic of individual groups and species, and is widely used in the systematics of spiders. The male fills the bulbs of the pedipalps with seed shortly after the last molt. The spermatic reticulum has a triangular or quadrangular shape and is suspended horizontally. In a drop of sperm allocated to her, the male immerses the ends of the pedipalps. It is believed that sperm penetrates through the narrow channel of the embolus due to capillarity, but it has now been established that at least forms with complex copulatory organs have a special seminiferous tubule. In some spiders, the male does not make a net, but stretches one or several cobwebs between the legs of the third pair, releases a drop of sperm onto the cobweb and brings it to the ends of the pedipalps. There are also species whose males take sperm directly from the genital opening. The male with sperm-filled copulatory organs goes in search of the female, sometimes overcoming considerable distances. At the same time, he is guided mainly by the sense of smell. He distinguishes the odorous trace of a sexually mature female on the substrate and her web. Vision in most cases does not play a significant role: males with smeared eyes easily find females. Having found the female, the male begins "courtship". Almost always, the excitation of the male is manifested in certain characteristic movements. The male twitches the threads of the female's web with his claws. The latter notices these signals and often rushes at the male as if it were prey, putting him to flight. Persistent "courtship", sometimes continuing for a very long time, makes the female less aggressive and prone to mating. Males of some species weave small "marriage nets" next to the female's nets, onto which they lure the female with rhythmic movements of the legs. For spiders that live in burrows, mating takes place in the burrow of the female. In some species, repeated mating with several males and rivalry of males are observed, which gather on the female's nets and, trying to approach her, fight with each other. The most active one drives away rivals and mates with the female, and after a while another male takes his place, etc. Each type of spider has its own characteristic form of “courtship”, or “dance”, males, according to the figurative expression of Millo, have their own “nuptial choreography". The larger predatory female spider is very aggressive towards the male, who approaches her with the greatest caution. It is believed that the complex forms of male behavior are aimed at overcoming the predatory instincts of the female: the male behavior differs sharply from ordinary prey. It is characteristic that in those cases where the sex relations are more peaceful, there are usually no “dances” or other warning movements of the male. In some species, the male mates with the newly molted female, when her integument has not yet hardened and she is helpless and safe. The behavior of partners after mating is different. In a number of species, the male is always the prey of the voracious female, and when the female mates with several males, she eats them one by one. In some cases, the male flees, showing amazing agility. A tiny male of one tropical cross, after mating, climbs onto the back of the female, from where she cannot reach him. In some species, partners diverge peacefully, and sometimes the male and female live together in the same nest and even share prey. The biological meaning of eating males by females is not entirely clear. This is known to be especially true for spiders that feed on a variety of prey, and is not common for species more specialized in choosing prey. In those spiders in which males can only mate once, but after mating continue to "courtship", competing with unmated males, their elimination by the female is beneficial to the species.

Eggs are laid a few days or weeks after mating. Fertilization occurs in the uterus, with which the seminal receptacles communicate. The masonry is placed in a cocoon made of cobwebs. Usually the female turns her lair into a nest in which eggs are laid and a cocoon is woven. As a rule, the cocoon consists of two gossamer plates, fastened with edges. First, the female weaves the main plate, on which she lays her eggs, and then braids them with the cover plate. These lenticular cocoons are attached to the substrate or wall of the nest. The walls of the cocoon are sometimes impregnated with a secret secreted through the mouth, impregnated with soil particles, plant residues. Most web spiders have a spherical cocoon, its tissue is loose and fluffy, resembling delicate cotton wool. Sometimes a dense outer shell is superimposed on top of the loose material. The female Pisaura weaves a spherical cocoon entirely, leaving a small hole on top through which she lays her eggs. Since spiders usually sit on nets with the ventral side up, they lay eggs and weave a cocoon in this position, hanging the cocoon on a stalk or thread. Dense cocoons, which reliably protect the clutch, are characteristic in those cases when they are placed outside the nest or the nest is unstable. When the nest is firmly and well camouflaged, the walls of the cocoon placed in it are thin, and sometimes there are only loose threads of the cobweb that hold the eggs on the wall of the nest. A thin-walled cocoon is usually made in those cases when the female guards it or carries it with her. The number of cocoons prepared by one female varies, often one cocoon, sometimes several, rarely more than a dozen. The number of eggs varies from 5-10 to several hundred, rarely up to 1000 (in some Araneidae). Cocoon sizes are usually from a few millimeters to 1-2 cm. The tiny spider Telema tenella from the Pyrenean caves makes cocoons 2 mm in size by placing one egg in them. Cocoons of large tarantulas come with a small tangerine. The color of the cocoon, if it is not masked by soil particles, is often white, but there are pink, golden yellow, green, striped cocoons. The females of some spiders make more complex cocoon nests. Thus, in Agroeca brunnea (family Clubionidae), the nest has the form of a closed goblet and is attached to the stem of the plant with a leg. It is divided into two chambers, in the upper one there are eggs, in the lower one there are hatched spiders for some time. Caring for offspring is very common among spiders and is most often expressed in the protection of the cocoon and caring for it. Females guard their cocoons in nets, mink or nest. In many stray spiders and some web spiders, females carry a cocoon with them, attaching it to spider warts or holding it in chelicerae. The female tarantula warms up the cocoon by turning it under the rays of the sun penetrating into the mink. When the spiderlings hatch, the mother helps them out by opening the seam of the cocoon. During the period of protection of offspring, the female usually does not eat anything, she loses a lot of weight, her abdomen shrinks. In some species, the female dies before the release of juveniles, and her shriveled corpse is found near the cocoon. Usually, after the juvenile leaves the cocoon, the female no longer takes care of her, but in some spiders, the juvenile climbs onto the mother's body and clings to her until she molts (family Lycosidae, etc.), or lives under her protection in the nest.

With all the diversity and complexity of caring for offspring, it is based on instinctive behavior, the expediency of which is violated under unusual circumstances. For example, if a cocoon is taken away from a female lycosid and replaced with another object of the same size, shape and weight, then she continues to wear this useless object. Interestingly, cuckoo spiders are known to throw their cocoons into other people's nests, leaving them in the care of other spider species. In general, the instinct to protect offspring is the weaker, the more reliable the construction of the nest or cocoon. In cases where the fate of the offspring is well guaranteed by a nest or a strong camouflaged cocoon, it is usually left without the care of the female. Hatching of juveniles from eggs of the same clutch occurs more or less simultaneously. Before hatching, the embryo is covered with a thin cuticle, spines are formed at the base of the pedipalps - “facial teeth”, with the help of which the facial membranes are torn. The hatched spider has thin covers, undivided appendages, is immobile and cannot actively feed. He lives off the yolk that remains in the intestines. During this yolk period of development, which varies in duration, the juveniles remain in the cocoon and molt (in different species from one to three times). In most spiders, the first molt occurs while still in the egg, so that the molted skin is shed along with the facial shells at hatching. Becoming more active, the spiders emerge from the cocoon, but usually they still stay together for some time. If you touch such a cluster, in which sometimes there are several hundred spiderlings, they scatter along the web of the nest, but then again gather in a dense club. Soon the spiders disperse and begin to live on their own. It was at this time that in a number of species, juveniles are dispersed on cobwebs through the air. Young spiders climb onto towering objects and, raising the end of the abdomen, release a web thread. With a sufficient length of the thread, carried away by air currents, the spider leaves the substrate and is carried away on it. Settling of juveniles usually occurs at the end of summer and autumn, but in some species in spring. This phenomenon is striking in the fine autumn days of "Indian summer". Particularly spectacular are the massive autumn flights of spiders in the southern Russian steppes, where sometimes you can see entire “flying carpets” several meters long, consisting of many tangled cobwebs, floating in the air. In some species, especially small ones, adult forms also settle on the web. Spiders can be lifted by air currents to considerable heights and transported over long distances. There are known cases of the mass appearance of small spiders flying onto ships hundreds of kilometers from the coast. Settled small spiders are similar in structure and lifestyle to adults. They settle in habitats characteristic of each species and, as a rule, from the very beginning arrange dens or weave trapping nets, which are typical for the species in design, only increasing them as they grow. Sometimes lifestyle changes with age. For example, young tarantulas lead a wandering daytime lifestyle, and when they grow up, they make a mink and become active at night. The number of molts during life varies depending on the final body size. Small species (5-6 mm) make 4-5 molts, medium (8-11 mm) - 1-8 molts, large (15-30 mm) - 10-13 molts. Males, which are smaller than females, also have fewer molts. Dwarf males of some species, leaving the cocoon, do not molt at all. In large tarantulas that live for several years, molting also occurs in adulthood once or twice a year after each breeding season.

4. Biological features

The body of the spider, like armor, is covered with an external skeleton (exoskeleton) formed by a solid substance - chitin. The exoskeleton is not elastic, therefore, as the spider grows, it periodically sheds the old “armor”, changing it to a new one.

The entire body of the spider is covered with various taste and tactile hairs. On the pedipalps and legs there are special hairs, trichobothria, which catch the slightest fluctuations in the air, warning of the appearance of prey or an enemy.

The spider is often weaker than the prey it hunts. Therefore, he uses a poison that kills or paralyzes the prey before it starts to resist. The poisonous glands of the spider are located in the chelicerae. Each of the two glands is surrounded by spiral muscles, during the contraction of which the poison is injected into the body of the victim through the claw-like segment.

The cephalothorax contains the brain, poisonous glands, stomach and muscles. The abdomen contains the heart, lungs, trachea, intestines, excretory system, spider glands and reproductive organs. The spider's stomach works like a pump, stretching out to suck in food crushed by chelicerae to a pulp.

Conclusion

Web adaptations represent evolutionary ranks from very simple to extremely complex and perfect, whether they are egg cocoons, lairs and nests, or trapping nets. At the same time, the chains of instincts aimed at creating web devices are becoming more complicated. It is remarkable that the general type of the structure of the spider is steadfastly preserved. The sizes of spiders, color, external form are very different, the structure of individual organs changes, but all this infinite variety is contained within the framework of a certain stereotype. A spider is always a spider. Unity is also maintained in a number of features of biology, type of nutrition, individual development, etc. Comparison with other arachnids is indicative. We have seen that each order also has its own stable type of organization, but at the same time, the species diversity of most orders cannot be compared with that of spiders. If we turn to another group of multi-species orders - ticks, then the abundance of species there is based on deep and various changes in organization and development, sometimes so much that you don’t immediately know whether it’s a tick or something else. In other words, mites, adapting to new conditions, changed greatly themselves, while spiders changed their web adaptations, while maintaining the type of organization.

Bibliography

1.Bei-Bienko G.Ya., Danilevsky A.S., Ivanov A.V. and others. Determinant of classes and orders of terrestrial arthropods. - M.; L.: Nauka, 1957.

2. Beklemishev V.N. Fundamentals of comparative anatomy of invertebrates. - M.: Nauka, 1964.

3. Blokhin G.I. , Aleksandrov V.A. Zoology.- "KoloS" 2005

4. http://ru.wikipedia.org/wiki/Spiders

5. http://dic.academic.ru/dic.nsf/enc_colier/1807/SPIDERS

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Classification

Fig.1. Representatives of arachnids

Spiders

This squad belongs to the predators. Some hunt their prey with sticky nets, while others build cone-shaped traps out of webs.

Ticks

This order includes small and microscopic arachnids. They eat both solid and liquid food. Some of them can cause significant damage to the crop due to damage to grains and plants. There are species that are carriers of dangerous diseases.

Fig.3. Ticks

scorpions

Atypical representatives of this class. The body of a small size (up to 20 cm) consists of three sections. At the end of the body in the tail section is a poisonous gland. Their victim is detected due to oscillatory movements. Scorpions breed depending on the species: there are viviparous, there are oviparous.

Fig.4. Scorpion varieties

haymakers

Representatives are very similar to spiders, but, unlike them, have a segmented abdomen. The limbs are long (up to 16 cm), there are claws at the ends, there are even double ones. They feed not only on the liquid contents of the victim, but also on small solid particles, which they pinch off with the help of chelicerae. Plants, mushrooms, fish, carrion, animal feces are consumed as food.

Fig.5. haymakers

What have we learned?

The arachnid class is one of the many representatives of the planet's fauna. There are over 100 thousand varieties of these animals in the world. An example is more than 40 thousand species of only spiders and the same number of species of acariform mites. Hardly any other class can boast such diversity.

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