The Tarantula (Family Theraphosidae)

In the Americas the term “tarantula” refers to any of about 300 species of primitive spiders with poor eyesight belonging to the family Theraphosidae, Suborder Orthognatha, Order Araneae. About 30 species occur in the United States. Many are among the largest of all spiders, weighing 2-3 ounces and with a 10-inch leg spread. They are typical mygalomorphs (fig. 1), generalized spiders whose mouth parts move up and down instead of from side to side as do most spider chelicerae. The term tarantula is derived from a city in Italy and truly belongs to a wolf spider of that area, Lycosa tarentula (linnaeus), which is itself deeply involved in folklore. The folklore was brought to the new world by immigrants who, as soon as they saw some of the big spiders of the American tropics and deserts, called them tarantulas. There also is a genus of tailless whip scorpions known scientifically as Tarantula, however, in North and South America “tarantula” is so firmly established as the name of the big, hairy mygalomorphs that there is little confusion in the use of the term. The rather large, longlegged, fast-moving spiders that are found frequently on shipments of bananas coming into Florida from Latin American countries … and believed by many people to be tarantulas…usually prove to be giant crab spiders of the family Heteropodidae. Their bite, like that of the tarantulas, may be temporarily painful but is only very mildly toxic to humans.

Because of their size and formidable appearance, tarantulas have the reputation of being deadly poisonous, so far as is known, this is not true, there are no verified records of human deaths caused by a tarantula, the species found in the united states are relatively harmless to humans; however, some South American species have caused localized toxic reactions which disappear within 3 days. Some species have killed both white rats and birds in experiments. William Baerg tested 26 species, many of these on himself. Of 9 species he induced to bite him, only 1 caused an observable reaction. The species Baerg tested were from various parts of the tropics, and many had been thought to be poisonous. While not all species have been tested scientifically, it is indeed questionable whether the bite of any species would kill or seriously injure a human. The bite may be rather painful for a brief period of time, since the fangs of the chelicerae are quite large, but the injury to humans is largely mechanical, with little, if any, noticeable toxic effect. Furthermore, tarantulas very seldom bite humans, even when handled frequently, and are considered by many people to make excellent pets, Baerg (1958) wrote, “to anyone who has learned to know this spider, it is as handsome as a goldfinch and fully as interesting.”

The dorsal surface of the abdomen of many new world tarantulas, in addition to a covering of longer sensory hairs (fig, 2), bears a dense covering of shorter specialized hairs called urticating hairs (fig. 3) that can provoke intense skin irritation in man on contact and which, presumably, provide tarantulas with a defense against some of their enemies. Cooke et al, (1972) published a detailed account of these urticating hairs, dividing them into 4 main types, based on a study of more than 40 species of tarantulas. They stated that the role of these minutely barbed hairs in nature is wholly defensive, apparently most effective against small mammals attacking spiders in their burrows. The spider defends itself by kicking the hairs loose with its hind legs. This explains why most tarantulas kept as pets have a bald spot on the back of the abdomen, presumably this defense mechanism does not protect the tarantula against its arch enemies, the Pepsis wasps, which successfully attack it even within its burrows, or from parasitic acrocerid flies. Cooke et al, (1972) wrote that the urticarious effect of the hairs seems to be due solely to mechanical irritation, and at the time it was published there was no evidence of any chemical irritant being involved. Baerg (1958) reported that rubbing the back of a tarantula against the skin of his forearm caused only a mild irritation that remained noticeable for about an hour, but that a similar test made on his wife produced more marked results, she felt a sharp irritation for several hours; subsequently there was a mild eruption of the forearm, appearing at irregular intervals over a period of several weeks. Interestingly, the minute details of urticating hairs of tarantulas, only recently revealed by the electron scanning microscope, provide reliable characters which promise to be of considerable value in the confused field of theraphosid systematics.