Spider (arthropod), any of a large group of invertebrates (animals without backbones) that have spinning glands used to produce silken threads and webs. There are about 40,000 species of spiders. Spiders are found worldwide, except for in the oceans, and they live in all habitats and at most elevations.
Spiders, along with daddy longlegs, mites, ticks, and scorpions, belong to a group of animals known as arachnids. Spiders are not insects. Spiders have a different body structure than insects. The bodies of spiders divide into two parts (a fused head and thorax and an abdomen), and spiders have eight legs and eight eyes; they lack antennae and wings. In contrast, the bodies of insects form three parts (head, thorax, and abdomen), and insects have six legs, two eyes, two antennae, and, typically, four wings.
All spiders are carnivorous (feeding mainly on the flesh of other animals). Spiders eat insects and sometimes other arthropods (invertebrate animals with jointed limbs, segmented bodies, and hard shells known as exoskeletons), including other spiders. Scientists often divide spiders into two types: web spiders and ground spiders. Web spiders produce webs to capture prey, while ground spiders hunt prey directly without using a web. Almost all spiders use poison glands to kill or paralyze their prey or to defend themselves.
Contrary to popular belief, most spider bites are not dangerous to humans. Of the 40,000 species of spiders, only about 30 species produce bites that may cause illness. Spiders rarely attack humans unless they feel threatened, and if they do bite, the wound is rarely serious. There is absolutely no reason to kill any spider or to call an exterminator if you have spiders in your house. As an old English saying goes, “If you want to live and thrive, let a spider run alive
Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.
