Spiders Are Insect’s Worst Nighmare

There are more than 46,700 species of arachnids that differ from insects in having eight legs rather than six and in having the body divided into two parts rather than three. The use of silk is highly developed among spiders. Spider behavior and appearances are very diverse throughout the world.

All spiders are predators, feeding almost entirely on insects. Some spiders are active hunters that chase and overpower their prey. These typically have a well-developed sense of touch or sight. Other spiders instead weave silk snares, or webs, to capture prey. Webs are instinctively constructed and effectively trap flying insects. Many spiders inject venom into their prey to kill it quickly, whereas others first use silk wrappings to immobilize their victims. It is estimated that the world's 25 million tons of spiders kill 400–800 million tons of prey per year. Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters utilize their very acute vision. 

Although most spiders are inconspicuous free-living terrestrial forms, a few spiders live on or near water. Most arachnids lead solitary lives, coming together only briefly for mating. Many arachnids are found only in well-protected habitats. Thriving in the relatively constant, moisture-containing microclimates provided by soil litter, burrows, or caves, arachnids make up a high proportion of the animals found in dark or otherwise hidden environments. Cave-dwelling species often have special adaptations such as long extremities, light color, and no eyes. Most arachnids, even those adapted to desert areas, avoid excessive heat by adopting a habit of being active only during the cooler parts of the day.

A few arachnids (e.g., some scorpions, sun spiders, spiders, and daddy longlegs) can produce rasping sounds by rubbing together horny ridges or other special sound-producing structures. Sound may be used in general to warn predators or by males during courtship. Preening is common among arachnids. In some species protection and escape from predatory enemies is made possible by the ability of a seized limb to detach from the body.