- The American tarantula is a large spider that can be found in the southwestern United States.
The spider is the most common and varied of all the land predators. A predator is an animal that hunts other animals for food. Spiders feed almost entirely on insects and are best known for making webs that catch their prey. Spiders differ from insects because they have eight legs instead of six. Also, their body is divided into two parts rather than three. Where spiders liveSpiders are found on all continents except Antarctica. They have even been found at elevations as high as 16,400 feet (5,000 meters) in the Himalayan ranges. Although most spiders live on land, one Eurasian species lives in slow-moving fresh water. The largest spiders, tarantulas, are found in warm climates and are most abundant in the Americas. The smallest spiders are found in the tropics. Physical characteristicsSpiders range in body length from 0.02 to 3.5 inches (0.5 to about 90 millimeters). Their bodies are divided into two parts, the cephalothorax and the abdomen. The legs are attached to the cephalothorax, which contains the stomach and brain. The top of the cephalothorax is covered by a protective structure, called the carapace. The underside is covered by a structure called the sternum. The abdomen contains the gut, the heart, the reproductive organs, and the silk glands. Unlike insects, spiders have no antennae. They do, however, have two appendages near their mouths that are often confused with insect antennae. These structures, called pedipalps, are used by spiders to manipulate their prey while feeding. Spiders also have four pairs of walking legs. Each leg has eight segments. The legs contain several types of sense organs and may have claws. A few species use the first pair of legs as feelers. Spiders usually have eight eyes. These are simple and not well developed. Other sense organs are long fine hairs on the legs that are sensitive to air currents and vibrations. Spiders smell with specialized hollow hairs found at the tips of the pedipalps and the legs. BehaviorSpiders are the only animals that digest their food outside their bodies. After their prey is captured, spiders cover it with digestive juices from their intestinal tract. The juices break down the prey's body into a liquid form that the spider sucks up. By repeating this process many times, spiders eventually digest the entire animal. Most spiders have venom glands that they use against predators. Although most spider venoms are not harmful to humans, those produced by the black widow and the brown recluse spider are. The venom of the black widow acts as a painful nerve poison. The venom produced by the brown recluse causes swelling and the death of tissues around the area where the poison was injected. Spiders are well-known for spinning silk. Although some insects such as centipedes and millipedes produce silk, only spiders are true silk specialists. More than seven different types of glands in the abdomen produce the silk. Ducts, or tubes, from the glands travel through structures called spinnerets, which open to the outside through spigots. Abdominal pressure forces the silk to flow outward. Spiders use silk for a variety of purposes in addition to weaving webs. They use silk to wrap their prey, protect their eggs, and make nests or line their burrows. Some spiders spin silk threads that stretch out from their burrows or nests. These silks act as signal lines that are triggered when an insect walks over them. |