On the abdomen are located modified appendages, the spinnerets, used in secreting silk. The digestive system of spiders is adapted exclusively to taking up liquid food, because the animals generally digest their prey outside the body and then suck the fluid. The fairly complex brain is larger or smaller in certain parts, depending on whether the animal locates prey mainly by touch or vision. Among arachnids, only male spiders possess a copulatory organ on the pedipalp, an appendage at the anterior of the cephalothorax. The spider exudes its silk through the spinneret appendages at the tip of the abdomen, and then further draws it out using its legs.
Spiders are generally carnivorous and feed only on living prey.
They can crush it with processes on the pedipalps, and the chelicerae almost always have glands that can inject a venom. The bite of some large spiders can be painful, but most species are too small to break human skin, and only a few are dangerous to humans. The latter are mainly the black widow spider and its close relatives, which are nonaggressive and bite humans only in defense. About 105 families of spiders are known, plus about 10 that are extinct. Two suborders are widely but not universally recognized.