Like all arthropods, the tarantula is an invertebrate that relies on an exoskeleton for muscular support. Like other Arachnida, a tarantula's body comprises two main parts, the prosoma (or cephalothorax) and the opisthosoma (or abdomen). The prosoma and opisthosoma are connected by the pedicel, or pregenital somite. This waist-like connecting piece is actually part of the prosoma and gives the opisthosoma a wide range of motion relative to the prosoma.
Tarantula sizes can range from as small as the size of a BB pellet to as large as a dinner plate when the legs are fully extended. Depending on the species, the body length of tarantulas ranges from 0.180 to 4.33071 in (5 to 110 mm), with leg spans of 8–30 cm (3–12 in). Some of the largest species of tarantula may weigh over 85 g (3 oz).
Most species of North American tarantulas are brown. Elsewhere, species have been found that variously display cobalt blue (Cyriopagopuslividus), black with white stripes (Aphonopelmaseemanni), yellow leg markings (Eupalaestruscampestratus), metallic blue legs with vibrant orange abdomen and green prosoma (Chromatopelmacyaneopubescens).
Tarantulas of various species occur throughout the United States, Mexico, in Central America, and throughout South America. Other species occur variously throughout Africa, much of Asia (including the Ryukyu Islands in southern Japan), and all of Australia. In Europe, some species occur in Spain, Portugal, Turkey, southern Italy, and Cyprus.
While they pose few threats to humans, they are fierce predators of insects, and some South American species even hunt birds and small mammals. When tarantulas are ready for a meal, they grab their prey and inject it with immobilizing venom. The spider then kills the prey with its fangs and secretes digestive enzymes so that their meal can be slurped into their mouth.
All tarantulas are venomous and some bites cause serious discomfort that might persist for several days. In general, the effects of the bites of all kinds of tarantula are not well known. While the bites of many species are known to be no worse than a wasp sting, accounts of bites by some species are reported to be very painful and to produce intense spasms that may recur over a period of several days. In all cases, seeking medical aid is advised.
Before biting, a tarantula may signal its intention to attack by rearing up into a "threat posture", which may involve raising its prosoma and lifting its front legs into the air, spreading and extending its fangs, and (in certain species) making a loud hissing by stridulating. Tarantulas often hold this position for longer than the duration of the original threat. Their next step, short of biting, may be to slap down on the intruder with their raised front legs. If that response fails to deter the attacker, the tarantulas of the Americas may next turn away and flick urticating hairs toward the pursuing predator. The next response may be to leave the scene entirely, but especially if no line of retreat is available, their final response may also be to whirl suddenly and bite. Some tarantulas are well known to give "dry bites", i.e., they may defensively bite some animal that intrudes on their space and threatens them, but they do not pump venom into the wound.
Most New World tarantulas are equipped with urticating hairs on their abdomens, and almost always throw these barbed bristles as the first line of defense. These bristles irritate sensitive areas of the body and especially seem to target curious animals that may sniff these bristles into the mucous membranes of the nose. Somespecieshavemoreeffective urticating bristlesthanothers.
Old World tarantulas have no urticating bristles and are more likely to attack when disturbed. They often have more potent, medically significant venom, and are faster and much more nervous and defensive than New World species.
After reaching sexual maturity, a female tarantula normally mates and lays eggs once per year, although they do not always do so.
As with other spiders, the mechanics of intercourse are quite different from those of mammals. Once a male spider reaches maturity and becomes motivated to mate, he weaves a web mat on a flat surface. The spider then rubs his abdomen on the surface of this mat, and in so doing, releases a quantity of semen. He may then insert his pedipalps (short, leg-like appendages between the chelicerae and front legs) into the pool of semen. The pedipalps absorb the semen and keep it viable until a mate can be found. When a male spider detects the presence of a female, the two exchange signals to establish that they are of the same species. These signals may also lull the female into a receptive state. If the female is receptive, then the male approaches her and inserts his pedipalps into an opening in the lower surface of her abdomen, the opisthosoma. After the semen has been transferred to the receptive female's body, the male swiftly leaves the scene before the female recovers her appetite. Although females may show some aggression after mating, the male rarely becomes a meal.
Females deposit 50 to 2,000 eggs, depending on the species, in a silken egg sac and guard it for six to eight weeks. During this time, the females stay very close to the egg sacs and become more aggressive. Within most species, the females turn the egg sac often, which is called brooding. This keeps the eggs from deforming due to sitting in one position too long. The young spiderlings remain in the nest for some time after hatching, where they live off the remains of their yolk sacs before dispersing.
Tarantulas may live for years; most species take two to five years to reach adulthood, but some species may take up to 10 years to reach full maturity. Upon reaching adulthood, males typically have but a 1.0- to 1.5-year period left to live and immediately go in search of a female with which to mate. Female specimens have been known to reach 30 to 40 years of age, and have survived on water alone for up to two years.
Tarantulas are easy to care for and need relatively little attention, but need it reliably throughout their long lives. Tarantulas cannot be released outside when you are tired of them.
Most tarantulas come from tropical areas, so need to be kept relatively warm and not left in chilly areas of your house. You would not want to carry one outside in the winter, even briefly, without wrapping the cage well. Surprisingly, because of their large size, tarantulas tend to be relatively delicate. The exoskeleton of the abdomen is relatively thin. If dropped, they tend to splat and bleed to death. For the spider’s sake, I strongly suggest not handling tarantulas. They are elegant, interesting animals, but not cuddly pets. Just as you would not expect to pet your fish, do not get a tarantula with the goal of handling it.
Care for tarantulas is relatively easy: feed them once or twice a week depending on their hunger levels, keep humidity high in the cage (if a tropical species), and make sure that there are no crickets in the cage when the spider moults or else the cricket will kill the spider. Crickets or flies are better than mealworms or superworms. Don’t let their cages dry out. Give them water. Your spiders do not need large cages and smaller animals will do better in smaller containers than larger ones. Keep them on a sterile substrate soil (potting soil without minerals added, vermiculite, commercial top soil, pet bark [not cedar], peat – NOT soil from your yard!) which can hold moisture. Provide retreats and some environmental enrichment (bark to climb on, something to hide under). Plants are for your aesthetics, not for the spiders. No sharp cactuses or other plants that can injure the spider.