Tarantulas comprise a group of often hairy and often very large arachnids belonging to the family Theraphosidae, of which approximately 900 species have been identified. Some members of the same Suborder may also be called "tarantulas" in the common parlance. This article will restrict itself to describing members of Theraphosidae.
Like all arthropods, the tarantula is an invertebrate that relies on an exoskeleton for muscular support. A tarantula’s body consists of two main parts, the prosoma (cephalothorax) and the opisthosoma (abdomen). The prosoma and opisthosoma are connected by the pedicle, or what is often called the pregenital somite. This waist-like connecting piece is actually part of the prosoma and allows the opisthosoma to move in a wide range of motion relative to the prosoma.
The biggest tarantulas can kill animals as large as lizards, mice, and birds.They can be found in the south and west parts of the USA, Central America, and down throughout South America to the southern parts of Chile, Argentina. Tarantulas can also be found throughout Africa, large parts of Asia and all over Australia. In Europe, there are some species in Spain, Portugal, Turkey, Italy, and in Cyprus. Most tarantulas are harmless to humans, and some species are popular in the exotic pet trade. All tarantulas are venomous, but only some species have venom that, while not known to have ever produced human fatalities, can produce extreme discomfort over a period of several days. Some genera of tarantulas hunt prey primarily in trees; others hunt on or near the ground. All tarantulas can produce silk while arboreal species will typically reside in a silken "tube tent", terrestrial species will line their burrows with silk to stabilize the burrow wall and facilitate climbing up and down. Tarantulas mainly eat insects and other arthropods, using ambush as their primary method of prey capture.
The eight legs, the two chelicerae with their fangs, and the pedipalps are attached to the prosoma. The chelicerae are two double segment appendages that are located just below the eyes and directly forward of the mouth. The chelicerae contain the venom glands that vent through the fangs. The fangs are hollow extensions of the chelicerae that inject venom into prey or animals that the tarantula bites in defense, and they are also used to masticate. These fangs are articulated so that they can extend downward and outward in preparation to bite or can fold back toward the chelicerae as a pocket knife blade folds back into its handle. The chelicerae of a tarantula completely contain the venom glands and the muscles that surround them, and can cause the venom to be forcefully injected into prey.