Spider - type class of arthropods. Its major representatives are the real spiders, Scorpions and mites (see).
Live on land, few people in the water. Spiders and Scorpions are predators that feed on insects. Bites of venomous spider (Latrodectus) and injections Scorpions cause people poisoning, sometimes severe. Ticks are parasites of humans and animals, spread of tick-borne relapsing fever (see), tick-borne encephalitis (see), tick-borne (Krasnoyarsk) typhoid fever, fever Rocky mountains and other diseases among the people; piroplasmosis and other diseases in domestic animals (see Carriers, Poisonous animals).

Arachnoids (Arachnida) - class invertebrates type Arthropoda, with about 35 000 species. Systematics arachnids are insufficiently developed. Class Arachnida include units: Scorpions (Scorpiones), salugi (Solifugae), kenaney (Palpigradi), monocompany (Pseudoscorpiones), spiders (Aranei, opiliones (Opiliones), ricinoleic (Ricinulei), telephony (Uropygi), Freni (Amblypygi), tartarini (Tartarides) and ticks (Acarina). Arachnoids are large morphological diversity. The body is divided into golovogrud and abdomen, rarely connected (ticks). The finiteness of the cephalothorax: chelicera, legs long and strong, and 4 pairs of legs. Antennae no, eye simple. The structure of the oral parts depends on nutrition. Covers formed chitinous cuticle. Some spiders are cancer: poisonous, odorous, spider. P. diclinous. Sexual dimorphism is more sharply expressed at spiders and mites. The majority P. lays eggs, some (Scorpions) viviparous.
Distributed on all continents; as a rule, terrestrial animals; only a few spiders live in water (water spider, water mites). In the bulk of predators, feeding on other arthropods, worms, mollusks. Among mites are bloodsuckers, a parasite of humans and animals.
P. are of great importance in human life. Ticks transmit to humans pathogens of diseases such as encephalitis, endemic ricketsiosis, tularemia and other Bites of some species of spiders are dangerous to human health. The greatest danger for humans and for animals (with the exception of sheep) represents the bite of the black widow (Latrodectus tredecimguttatus), distributed in southern areas of the USSR. Especially poisonous females these spiders in the spring-summer period. Local reaction from the bite of the black widow is poorly expressed, the poison has a strong neurotoxic effects. Less dangerous bite great steppe tarantula (Lycosa singoriensis), accompanied by pain and inflammation at the site of the bite. Injections of Scorpions (birth Buthus and Euscorpius)living on the territory of the USSR, for the life of man is not dangerous, but painful and in severe cases are accompanied by General phenomena of poisoning (see Poisonous animals). The entire squad Solifugae) poisonous glands do not have. If after a sting of the phalanx there is inflammation, it is explained by the pollution of the chelicerae. Some spiders, exterminating insects,is useful.