Spiders have two body regions: the cephalothorax and abdomen (insects have three regions: head, thorax, and abdomen). Spiders breathe through two pairs of lungs that open on the underside of their abdomens. The abdomen has specialized glands and structures for making and manipulating silk.
Spiders are predators of insects, sowbugs, and even other spiders. Some hunt during the day, some at night; some spiders specialize in capturing crawling insects, others in those that ﬂy. Most spiders can deliver a poisonous bite, but few have mandibles that can penetrate human skin; when they do, the venom is usually harmless.
Spider bites are similar to mosquito bites: there is a small swelling and itching for a short time.
A characteristic feature of spiders is their ability to produce silken threads by glands in the abdomen. Spider silk is a protein material with the strength of nylon, but it can be stretched by 31%, compared with only 16% for nylon. The silk is used to construct a snare to catch ﬂying insects. The spider remains in or close to the elaborate web to quickly capture and feed on the prey. The most recognized webs are those made by the orb weaver spiders; these can measure several feet in diameter.
Centipedes have one leg per segment, and the number of legs ranges from 15 to 181. The first body segment behind the head contains poison claws that are used to capture prey. These arthropods are nocturnal and occur in moist habitats. Most centipedes are predators of insects. The house centipede is the most common indoor centipede. It is fast moving and can climb walls and ceilings; it is a predator of spiders and small insects. These centipedes have 15 pairs of very long legs. The long antennae move in a whip-like manner over the body.
Millipedes have two pairs of legs on most of their body segments, and they have numerous body segments. They range in color from reddish orange to dark brown and black. Millipedes typically occur in moist or wet habitats. Many species curl up or form a compact spiral when disturbed. Food for millipedes is a variety of decomposing plant and animal material.