Terrific Tarantulas

Robert J. Wolff, Ph.D.
From the Biology Department,
Trinity Christian College, Palos Heights, Illinois 60463

The name "tarantula" means a variety of things to different people. It can mean the wolf spider from southern Italy, with its somewhat toxic bite, or the tailless whipscorpions, who belong to the family Tarantulidae. Or to many people, tarantula simply means any large, frightening spider they come across. Primarily, however, tarantula means the generally large, hairy spiders that belong to the family Theraphosidae. Spiders belong to the order Araneae, and the majority are considered true spiders, whose fangs point to the midline and open sideways. In contrast, fangs of the order Mygalomorphae open parallel to the long axis of the body. Mygalomorphs include the trapdoor and purseweb spiders, as well as those that are commonly called tarantulas and belong to the Theraphosidae. Structure Tarantulas are hairy, large (35 mm or more in length), and have the basic morphology of the true spiders (Fig. 1), including two body regions, the cephalothorax (prosoma) and the abdomen (opisthosoma). The appendages of the cephalothorax include four pairs of legs, a pair of pedipalps, and a pair of fang-tipped chelicerae. The abdomen differs from that of the true spiders by having posteriorly only two pairs of spinnerets rather than three pairs, and by having ventrally two pairs of booklungs rather than one pair. Figure 1 Tarantulas share the same basic morphology as true spiders.

You can usually identify mature males by the special copulatory organs (palps) on the pedipalps, and by the hooks on the first pair of legs (Fig. 2). Adult females are not as easily identifiable because they often lack obvious external clues; only size and (in some) a swelling in the genital area at the ventral slit, called the epigastric furrow, allow a guess. Figure 2 Mature male tarantulas can be identified by the hooks on the first pair of legs. Behavior Tarantulas may reach sexual maturity in as few as two years (fast-growing arboreal species in the tropics), or in as many as nine years (burrowing species). Males do not molt after reaching maturity, and soon after, adults usually begin wandering in search of females. Before copulation, a male takes up into his palps sperm that he has deposited on a specially spun sperm web. During copulation, he inserts the sperm into the female's genitalia. Males do not live more than a few months after mating. Females live longer, often reaching beyond 25 years in an appropriate environment. Tarantulas will normally eat any prey in the right size range, including most insects, other invertebrates, and even some small vertebrates. Tarantulas may specialize on certain prey, such as millipedes or desert beetles. Based on the little research that has been done, you should feed tarantulas a variety of insects to ensure that they obtain all the needed nutrients. Normally, feeding twice a week is enough, but any live insects still not eaten within a day should be removed from the aquarium. Go to next page...