Tuesday, March 3, 2009

The Brief Desciption of Spider

This is the basic lesson before you know deeper about spider, we start from desciption. Spiders are air-breathing arthropods chelicerate have eight legs, fangs and chelicerae modified injecting poison. In their bodies the usual arthropod segments are fused into two tagmata, cephalothorax and abdomen, along with a small, cylindrical pedicel. In all but the most primitive, the Mesothelae, spiders have most of the central nervous systems of all arthropods, as all nodes are merged into one mass in the cephalothorax. Spiders do not have the extensor muscles of the extremities and spread rather than hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk of up to six types of silk glands in their abdomens. Spider webs vary widely in size, shape and amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms and producing tangled cobwebs spiders are more abundant and varied ob-spiders. Spider-like arachnids with silk-producing spigots appear in the Devonian period some 386 million years ago, but apparently these animals lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years and are very similar to the most primitive to survive, Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic period, before 200 million years ago.

Spiders was described as vegetarian species in 2007, but all other known species are predators, preying mostly on other insects and spiders, though a few large species also birds and lizards. Spiders use a wide range of strategies to capture prey, the nets catch on sticky, sticky balls with lassoing imitating the prey to avoid detection, or running down. Most detect prey primarily by detecting the vibrations, but are active hunters acute vision, and the hunters of the genus Portia show signs of intelligence in the choice of tactics and the ability to develop new ones. Spiders "casings are too narrow to take solid food and liquidize by flooding with digestive enzymes and grinding with the foundations of their pedipalps, as they have no true jaws.

Male spiders identify themselves by a variety of complex courtship rituals to avoid being eaten by the females. Males of most species survive a few links, mainly limited by its short life. The women weave silk egg cases, each of which can contain hundreds of eggs. The females of many species care for their young, for instance, about carrying them or by sharing food with them. A minority of species are social, building community networks that can be anywhere from home to some 50,000 individuals. Behavior ranges from precarious social tolerance, as in the aggressive widow spiders, a cooperative hunting and sharing food. Although most spiders live in more than two years, mygalomorph tarantulas and other spiders may live up to 25 years in captivity.

While the venom of some species is dangerous to humans, scientists are now investigating the use of spider venoms in medicine and no pollutants such as pesticides. The spider silk offers a combination of lightness, strength and elasticity that is higher than that of synthetic materials and the spider silk genes have been inserted in mammals and plants to see if they can be used as a silk factory. As a result of its wide range of behaviors, spiders have become common symbols in art and mythology, which represent different combinations of patience, cruelty and creativity.

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