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EVERYTHING YOU WANT TO KNOW ABOUT SPIDERS
MORPHOLOGY AND GENERAL TAXONOMIC CHARACTERS OF SPIDERS
IMPORTANCE OF SPIDERS IN NATURE
HABITS AND HABITATS OF SPIDERS
SPIDER VENOM AND VERY POISONOUS SPIDERS
PROTECTIVE COLOURATION AND MIMICRY IN SPIDERS
COURTSHIP BEHAVIOUR IN SPIDERS
PARASITES AND OTHER ENEMIES OF SPIDERS
COLLECTION AND PRESERVATION OF SPIDERS
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Spiders together with scorpions, whip-scorpions, solpugids, ticks, mites and daddy-long-legs, belong to the Class Arachnida, which has 10 orders. The spiders have been kept in the Order Araneae. They may be readily separated from the daddy-long-legs (harvestmen) with which they are often confused by the fact that the latter have the abdomen noticeably segmented and broadly jointed to the cephalothorax and also lack the spinnerets at the hind end of the abdomen.
Spiders are not insects. They can be easily distinguished from the insects by the fact that they have eight legs and their body is divisible into two halves, cephalothorax and abdomen, joined together by a narrow stalk, while the insects have only six legs and their body is divisible into three halves, head, thorax and abdomen.
KINGDOM : ANIMALIA
PHYLUM : ARTHROPODA (Animals with jointed appendages)
CLASS : ARACHNIDA (Eight legged animals)
ORDER : ARANEAE (Animals possessing spinnerets, i.e., spiders)
MORPHOLOGY AND GENERAL TAXONOMIC CHARACTERS OF SPIDERS
The body of the spider is divisible into two distinctive parts, cephalothorax and abdomen joined together by a narrow pedicel. The cephalothorax is covered dorsally by a hard sclerotic shield, the carapace and ventrally by sternum. The anterior region of cephalothorax is called the cephalic region bearing the eyes and the posterior region is called the thoracic region which generally bears a depression in the middle called the thoracic groove.
On the cephalic region are present generally eight and sometimes six simple eyes. The eyes are of two types - black or diurnal eyes and white or nocturnal eyes. When both these types of eyes are present in a spider, the condition is called heterogeneous and when only one type of eyes are present, the condition is termed homogeneous. Generally the eyes are arranged in two rows, four eyes in each row. According to their position, the four pairs of eyes are termed anterior medians, anterior laterals, posterior medians and posterior laterals. The area margined by the four median eyes is termed the median ocular quadrangle.
The area between the anterior row of eyes and the base of chelicerae is the clypeus. The chelicerae are the first pair of appendages of the cephalothorax, each chelicera bearing a curved fang as its apex. The pedipalps are the second pair of appendages. Each pedipalp is composed of six segments; coxa, trochanter, femur, patella, tibia and tarsus. In mature males, the tarsus of palp is modified to carry a more or less complicated copulatory organ.
The legs are eight in number and are attached on the base of cephalothorax. Each leg is composed of seven segments; coxa, trochanter, femur, patella, tibia, metatarsus and tarsus.
The abdomen is produced posteriorly into a conical anal tubercle and bears three pairs of spinnerets ventrally; the first or the anterior pair, the second or the median pair and the third or the posterior pair. In a number of families, there is present, in front of the spinnerets, a seive-like plate, called the cribellum. A conical appendage called the colulus, lies between the bases of the anterior spinnerets.
The ventral surface of abdomen is provided with slits for one or two pairs of lung-books, followed by one or two paired spiracles. The female genital opening is the vulva or epigyne, with a transverse fold, known as epigastric furrow.
Spiders are exclusively carnivorous and predate mainly on insects. The spiders are one of the most important agents in nature which keep the insect populations in check and thus balance their ecosystems. A large number of spiders feed on insects like houseflies and mosquitoes which are carriers of serious diseases in human beings. Heteropoda, a house spider actively predates on cockroaches, the most persistent pests. A large number of spiders are found in agricultural fields and this suggests that they play an important role in controlling the population of many agricultural insect pests.
Spiders are a group of animals that are often neglected due to ignorance and fear and above all on aversion towards them. The widespread conception that spiders are highly poisonous, noxious and ugly is pure prejudice as it has been proved that although almost all spiders have poison glands, very few are dangerous to man.
Spiders are one of the most diverse animal groups in the animal kingdom. Many different types of spiders can be easily found even in a small area. They come in different sizes, sport myriad colours and are found in strikingly different habitats. Generally speaking, spiders are of two types - hunting spiders and web builders. The trap-door spiders dig holes in the ground and a few spiders are even capable of swimming.
According to the latest estimates, approximately 37300 species of spiders belonging to 3450 genera and 108 families are known from all over the world. It is believed that these figures represent only about one-fourth of the total number of spider species present in nature. Over 1000 species of spiders belonging to 236 genera and 44 families are so far known from the Indian subcontinent.
HABITS AND HABITATS OF SPIDERS
HABITS OF SPIDERS
Spiders are exclusively carnivorous in habit and in fact generally catch only live animals, the spider's attention being attracted by the movement of the prey. Most species are not particular as to the insects eaten but will take whatever happens to come their way. However, some species show the habit of feeding only on particular insects.
In the case of wandering and trap-door spiders, the prey is not wrapped in silk, but simply seized, held by the mouthparts, and eaten. Web builders generally enswathe the insect caught in their snares, then bite it, and later drag it to the hub, or to the retreat, to be eaten.
There are two ways in which spiders ingest food. Those with weak jaws puncture the body of the insect with their fangs and then slowly alternate between injecting digestive fluid through the hole and sucking back the liquidified tissues, until there remains but an empty shell. The tarantulas, wolf spiders, large orb-weavers and others with strong jaws mash the insect to pulp between the jaws, as the digestive fluid is regurgitated over it.
Spiders may feed on other spiders, and because of this tendency to cannibalism, a social life is hardly to be expected. Yet instances of commensalism are known. Many members of the genus Stegodyphus socialis live in a common large web. Small spiders of the genus Conopistha usually inhabit the snares of larger spiders and consume small insects which are neglected by the web's owner
HABITATS OF SPIDERS
Spiders inhabit diverse habitats. They may be found almost everywhere; on or near water, in or on the ground, from underground caves to the top of mountains. Some kinds of spiders live inside human habitations, others frequent the outside of structures. Tall and low plants have spider tenants, as do the dead leaves on forest floors, and the curled, dried leaves on trees in winter. Under bark, under stones, under fallen logs, these are only a few of their varied habitats.
Trap door spiders dig holes in the ground. The wolf spiders and tarantulas may make use of shallow holes in which to hide. Many of the gnaphosids, and some clubionids run about over the ground and are found under stones in meadows and in woods. A large number of spiders are found among and under loose rock formations. Many spiders prefer dark and shaded locations, where the humidity is high.
Some species are found along the edges of streams and ponds, over the surface of which they run, and beneath the surface of which they can dive, e.g., Pirata and Dolomedes. Some species like Pachygnatha and Tetragnatha species also prefer water courses, but are usually found on the shrubbery which overhangs the ponds or streams.
Other species are found in tall grass, on bushes and trees. Some over the branches and trunks, and hide under loose bark and in crevices. Snares may be built among twigs, and many linyphiids, theridiids and orb-weavers construct their webs in tall grass, bushes and foliage.
SILK OF SPIDERS
The silk of spiders is a fibroprotein which is produced as a liquid in varied and voluminous abdominal glands, that open out through the spinnerets at the posterior end of the spider's body. When drawn out of the spinnerets, the liquid ordinarily hardens to form the familiar silken threads. Silk may stretch as much as much as one-fourth its length before breaking, and the silk of Nephila is the strongest natural fibre known.
The silk organs of spiders are the most complicated silk glands placed inside the abdomen. The spiders spin many different kinds of silk and seven different kinds of silk glands are recognized.
USES OF SPIDER SILK
The very name spider, refers to its spinning habit, though the making of a snare is not the only use to which the spider puts its silk. The wandering spiders build no snares yet use the silk in various ways. Most spiders as they move about pay out a drag-line behind them and it is this type of line which supports the spider should it loose its footing or jump from a support. At frequent intervals the drag-line is fastened to the substratum by a large number of looped threads. This is called an attachment disc and it is from this point that the spider is supported should it drop on its drag-line.
Prey may be wrapped by a swathing band composed of numerous strands. Many spiders build a nest or retreat, which may be a tube open at both ends, a silk-lined excavation or an inverted cup near the web. The same or similar nests may be constructed for moulting, mating or hibernating. The females make egg sacs, and the males sperm webs. The snares may be irregular meshes, as in the Theridiidae, sheet-webs, as in the Linyphiidae, funnel-webs, as in the Agelenidae, orb-webs, as in Araneidae and Tetragnathidae, or combination of two or more of these.
One of the most interesting uses to which silk is put is by some spiders is a balloon. The spider climbs up high on a blade of grass, on a fence, or pole, and facing the wind stands on the tips of the tarsi and tilts the abdomen upwards. From the spinnerets are emitted threads which are paid out as the air currents pull, until the buoyancy of the parachute is enough to support the spider, which releases its hold and is carried away in the breeze.
The eggs are always laid within a cocoon of silk, though in some like Pholcus and Scytodes, both of which are house spiders, this may be quite scanty. The eggs of running spiders are laid upon a sheet of silk which is then wrapped around the egg mass, or another sheet is made over the eggs.
The araneids build orb-webs having geometrical precision and beauty. The characteristic feature of an orb-web is the central portion. It is lying within the supporting framework, consists of series of radiating threads of non-viscid and non-elastic silk. These threads support a continuous thread of viscid and elastic silk which is spun spirally from periphery to the web-centre. The web-centre and pattern of viscid spiral are highly variable and often specific to different genera. It is also noticed that as the spiderlings become mature, they go on changing their web-building patterns.
All spiders, with the exception of the members of only two small families, have poison glands. These glands open by a pore near the tip of each cheliceral fang. The gland itself is more or less cylindrical, and covered by a layer of spirally arranged muscles which contract to expel the venom.
The venom is apparently used by the spiders to kill their prey, and as a means of defence. The quantity ejected can be controlled by the spider, and may vary with the latter's age and physiological condition, as well as with the degree of irritation to which the spider is subjected. Most spiders are too timid and do not attempt to bite even when handled roughly. Nevertheless, there are some spiders that have been troublesome to man, and produce symptoms of what in the medical literature has been called arachnidism.
Apparently all spiders of black widows (Latrodectus) are known to cause illness. The venom is neurotoxic, and produces symptoms like painful rigidity of the abdominal wall muscles, tightening of chest, increase in blood pressure, profuse perspiration, nausea, localized edema etc. Treatment consists of the application of an antiseptic and an intravenous injection of 10% calcium gluconate to relieve muscle pain. Other examples of harmful spiders are Loxosceles reclusa, L. deserta, L. arizonica and L. laeta from South America.
Majority of the spiders found in nature are not harmful to man and should not be feared. Uptill now, there is no record of any man having died of spider bite.
PROTECTIVE COLOURATION AND MIMICRY IN SPIDERS
Protective colouration or camouflaging colouration is the harmony of colour, tone and shade of the body of an animal with its surrounding, so that it is indistinguishable from the background. In many cases, this is closely associated with a natural phenomenon called mimicry, in which, an animal resembles or imitates another animal, plant or other natural object not only in colouration but also in shape, size, appearance, surface structure and other details.
Many spiders are not only coloured like their surroundings but are of a peculiar body form resembling inanimate objects. Some like Thomisus resemble a piece of bird droppings and some like Hyptiotes appear like the buds of the plants on which the web is built. Many spiders with elongated body and legs resemble pieces of straw and grass.
Some spiders resemble other animals and of these mimics, the ant like species are most common. Examples are known in many families and often the mimicry extends not only to the body form but also to the behaviour, the spiders moving about with anterior legs elevated like a pair of antennae. Jumping spiders belonging to the genus Synemosyna are very good ant mimics.
COURTSHIP BEHAVIOUR IN SPIDERS
Among the remarkable phenomena occuring in spiders ranks the peculiar behaviour associated with mating. When the male matures, considerable effort is put forth in locating the female, which means that even the web building species now becomes a wanderer like the hunting spiders. As a rule, in the web-building species, the male signals by tweaking the threads of the female's snare. It is in the wandering spiders that courtship is most marked. This is particularly true of those families with relatively keen eye-sight. Here the male may dance before the female, wave the palpi, or legs, or both, and strike peculiar attitudes. It has been assumed that all of this serves to gain recognition by the female as well as to stimulate her. The male's behaviour eventually leads to a lulling of the female's normal instinct to consider him a prey and she submits to his advances, subdued by the ardour of the sexual impulse. It is interesting to note that the male of a European pisaurid actually presents the female with insect food, thus ensuring his own safety.
It is a popular misconception that the male is always killed by the female after the mating act is over. Actually, in only a very few species can this be considered the general rule. For the great majority, the sexes separate amicably and the male may even mate again later with the same or other females. Numerous instances are known of male and female sharing the same web, or same retreat, for considerable periods of time.
PARASITES AND OTHER ENEMIES OF SPIDERS
A number of hymnopterous insects parasitize the egg-sacs of spiders and some are found as external parasites on the body of spiders. There are also flies belonging to Order Diptera which eat the eggs of spiders, and some which are internal parasites in the body of spiders. Many animals which are predacious on insects are predators of spiders as well, and this include spiders themselves. Perhaps the most serious enemies are the wasps of the Families Psammocharidae and Sphecidae.
Wasps of some species prey only on spiders belonging to particular families or genera. Such wasps sting and paralyze the spider and then carry it to their previously excavated burrow where they lay an egg on it. The wasp larva feeds on the paralyzed spider, eventually to pupate and metamorphose into an adult.
COLLECTION AND PRESERVATION OF SPIDERS
COLLECTION
Spiders should be looked for in a variety of habitats. One of the methods employed to get spiders in large numbers is to use a sweeping net through tall grass, bushes and foliage and then picking out the spiders from among the insects, leaves and debris that was gathered along with them.
Bushes can be beaten and small trees shaken, after first putting down a light-coloured cloth or an inverted umbrella to make visible the specimens that drop. Spiders should be looked for under stones, on bark of trees and in cracks and crevices in soil debris and other structures.
One technique to collect wandering spiders is to use pit-fall traps. These are large cylindrical cans set into the ground such that the top is flush with the ground level. The can is loosely covered with a flat stone or a piece of plywood to keep out large predators and rain.
Specimens can be picked up with forceps, or with fingers, and for tiny species, a hair brush moistened with the preserving fluid is satisfactory.
PRESERVATION
After collection, a spider is transferred to the jar of preserving fluid. It is convenient to collect spiders in a dry vial of the proper size, if it has to be kept alive.
For the permanent preservation of spiders in a collection, 70% ethyl alcohol is a good preserving fluid. Sufficient quantity of alcohol should be used for the size of the specimen, since the body fluids dilute the preserving fluid.
A paper label bearing the name of the place and the date of collection, as well as the collector's name should be put inside the jar containing the spider in preserving fluid.
ACTINOPODIDAE
AGELENIDAE
AMAUROBIIDAE
AMMOXENIDAE
AMPHINECTIDAE
ANAPIDAE
ANTRODIAETIDAE
ANYPHAENIDAE
ARANEIDAE (ORB-WEAVERS)
ARCHAEIDAE
ATYPIDAE
AUSTROCHILIDAE
BARYCHELIDAE
CAPONIIDAE
CITHAERONIDAE
CLUBIONIDAE
CORINNIDAE
CRYPTOTHELIDAE
CTENIDAE
CTENIZIDAE
CYATHOLIPIDAE
CYBAEIDAE
CYCLOCTENIDAE
CYRTAUCHENIIDAE
DEINOPIDAE
DESIDAE
DICTYNIDAE
DIGUETIDAE
DIPLURIDAE
DRYMUSIDAE
DYSDERIDAE
FILISTATIDAE
GALLIENIELLIDAE
GNAPHOSIDAE
GRADUNGULIDAE
HAHNIIDAE
HALIDAE
HERSILIIDAE
HEXATHELIDAE
HOLARCHAEIDAE
HOMALONYCHIDAE
HUTTONIIDAE
HYPOCHILIDAE
IDIOPIDAE
LAMPONIDAE
LEPTONETIDAE
LINYPHIIDAE
LIOCRANIDAE
LIPHISTIIDAE
LYCOSIDAE (WOLF-SPIDERS)
MALKARIDAE
MECICOBOTHRIIDAE
MECYSMAUCHENIIDAE
MICROPHOLCOMMATIDAE
MICROSTIGMATIDAE
MIGIDAE
MIMETIDAE
MITURGIDAE
MYSMENIDAE
NEMESIIDAE
NEOLANIDAE
NESTICIDAE
NICODAMIDAE
OCHYROCERATIDAE
OECOBIIDAE
OONOPIDAE
ORSOLOBIDAE
OXYOPIDAE (LYNX-SPIDERS)
PALPIMANIDAE
PARARCHAEIDAE
PARATROPIDIDAE
PERIEGOPIDAE
PHILODROMIDAE (CRAB-SPIDERS)
PHOLCIDAE (DADDY-LONG-LEG SPIDERS)
PHYXELIDIDAE
PIMOIDAE
PISAURIDAE
PLECTREURIDAE
PRODIDOMIDAE
PSECHRIDAE
SALTICIDAE(JUMPING-SPIDERS)
SCYTODIDAE
SEGESTRIIDAE
SELENOPIDAE
SENOCULIDAE
SICARIIDAE
SPARASSIDAE
STENOCHILIDAE
STIPHIDIIDAE
SYMPHYTOGNATHIDAE
SYNOTAXIDAE
TELEMIDAE
TENGELLIDAE
TETRABLEMMIDAE
TETRAGNATHIDAE
THERAPHOSIDAE
THERIDIIDAE(COMB-FOOTED SPIDERS
THERIDIOSOMATIDAE
THOMISIDAE(CRAB-SPIDERS)
TITANOECIDAE
TRECHALEIDAE
TROCHANTERIIDAE
ULOBORIDAE
ZODARIIDAE
ZORIDAE
ZOROCRATIDAE
ZOROPSIDAE