Tarantulas are mygalomorphs (suborder Orthognatha), and thus they have jaws that move forward and down (rather than sideways and together, which is characteristic of araneomorphs [suborder Labidognatha]). Tarantulas are distinguished from other mygalomorphs by a collection of traits that include not only their size and hairiness but also their two pairs of book lungs and their three-segmented spinnerets. While the behaviour of tarantulas can vary, many make burrows in soil and feed mainly at night on insects and occasionally small frogs, toads, and mice. Theraphosids are generally harmless to humans, although they can inflict painful bites if provoked. They are often kept as pets.
In the southwestern United States, species of the genus Aphonopelma can attain a body length up to 5 cm (almost 2 inches) and a leg span up to 12.5 cm (almost 5 inches). The spiders, dark in colour and sluggish in movement, have a hairy body and hairy legs. The most common member of that genus is A. californicum (Eurypelma californicum; sometimes E. californica), which is found in California, Texas, and Arizona. A 30-year life span has been recorded for one individual of that species.
The largest species of tarantulas are found in South America and belong to the genus Theraphosa. The goliath bird-eating spider (T. leblondi or T. blondi) has a body length up to 7.5 cm (almost 3 inches) and in rare instances has been known to capture and eat small avian prey. Both the pinkfoot goliath (T. apophysis) and the goliath bird-eating spider can attain leg spans of about 30 cm (12 inches). The pinkfoot is distinguished by its pale pink feet, which fade when the spider molts.
The name tarantula was originally given to the wolf spider, Lycosa tarentula, of southern Europe and was derived from the town of Taranto, Italy. The bite of L. tarentula was once thought to cause a disease known as tarantism, in which the victim wept and skipped about before going into a wild dance (see tarantella). It has been shown, however, that the bite of L. tarentula is not dangerous to humans and that no ill effects can be attributed to it. The body of L. tarentula is about 2.5 cm (1 inch) long. Like other wolf spiders, it spins no web but catches its prey by pursuit.
Other spiders belonging to the same family as the New World tarantulas are the monkey spiders of Africa and the bird-eating spiders of Australia and New Guinea. Trap-door spiders and the dangerous funnel-web spider of Australia are also related to the theraphosids as members of Orthognatha.
Thanks to BBC EARTH for the Amazing Tarantula GIFS:
Fun Facts About Tarantulas: