Spiders come in a wide variety of shapes, colors, and sizes. Certain orb web spiders from Samoa are as small as a pinhead, while the Goliath bird-eating tarantula can have a leg span of more than ten inches. Tarantulas are in the superfamily Avicularioidea and are generally considered separate from “true spiders,” which are in the superfamily Argiopoidea.
All spiders are carnivorous. Most eat small insects, but many will eat other spiders, sometimes even ones of their own species. Some larger species of tarantula will eat vertebrates on occasion.
Instead of chewing, spiders use another technique to swallow prey. Their mouths are designed to ingest only liquid food, so they use venom to liquefy the tissue of their prey, which they can then swallow.
Spiders use a variety of methods to capture prey. The majority are web-builders, such as the golden orb weaving spider. They wait for insects to get stuck in their web and then pounce on them.
Some—wolf-spiders, jumping spiders—are considered wandering spiders because instead of building a web and waiting, they actively hunt prey. Others—certain crab-spiders and some species of the genus Misumena—ambush prey by hiding in flowers and killing the insects that come to pollinate them. Commensal spiders (species of the genus Argyrodes) live in the webs of larger species and feed on the smaller insects with which the web’s owner doesn’t bother.
Spiders can be found everywhere from coastal areas to mountainous regions, even in harsh deserts. The only places spiders do not live are in the polar regions, at the peaks of the world’s tallest mountains, and in open waters of the ocean.
Spiders live in a huge variety of habitats: in thick shrubbery, high up in trees, in pastures, beneath stones and fallen trees, in burrows beneath the soil, and even in rock and coral crevices on coastlines. Because of their increasing contact with humans, many spiders now live in the corners of buildings and other man-made structures.
The body, covered with a protective shield called the exoskeleton, is divided into two sections: the cephalothorax (a fusion of the head and thorax) and the abdomen.
Spiders have up to eight eyes, although many species have just six. On the head region of the cephalothorax is the spider's chelicerae, which are a pair of appendages used to seize and kill prey. At the end of these limbs are fangs, which contain poison glands used by spiders to inject venom. Also attached to the head region is a pair of pedipalps, which are short, leg-like appendages, which are used to manipulate prey.
The thorax region of the cephalothorax is host to the spiders’ four pairs of legs. After the cephalothorax is the spiders’ abdomen, which is covered in spiracles—tiny openings used for respiration. The abdomen also is where spiders have their web-producing spinning organs.
Growth and Development
Spiders use the numbers game to reproduce. They lay massive egg sacs, which are usually protected by a covering of silk and affixed to the web or another surface. In some species, the female carries the egg sac on her back. These sacs can hold up to several hundred eggs.
Once hatched, spiders molt their outer layer multiple times before they reach their full size. Molts generally occur four to 12 times during a spider’s lifespan, although the number and frequency differ among species. If a spider has lost a limb, it can usually regenerate it as long as it is young and still molting.