Tarantulas! The very mention of these large, hairy spiders can bring chills of fear and disgust to many people and of course prompt the question, “Why on earth would you want to keep THAT as a pet?” The answer is that tarantulas are fascinating spiders that have intrigued naturalists and hobbyists for years, and they actually do very well as household pets.
For more than twenty-five years, the hobby of keeping tarantulas has been growing in numbers and in importance in theUnited States, Europe, andJapan. Today, it is possible to purchase specimens from about a hundred species from around the world, a quarter of these in the form of captive-bred young. Yet tarantulas still are misunderstood by many pet keepers and sellers; a surprising number, perhaps a quarter of those reaching the wholesaler, die each year from poor caging and from a misunderstanding of their basic needs. If kept properly, tarantulas can be excellent pets that are easy to care for and feed and that may even breed in their cages.
Where Tarantulas Fit
Tarantulas are simply spiders—big and primitive spiders. They belong to the order Araneae (the spiders) of the phylum Arthropoda (invertebrate animals with jointed legs, including the insects, crustaceans, and even trilobites), and to the class Arachnida, a large assemblage of animals including such diverse groups as the scorpions, solpugids, and mites. Like insects and millipedes (class Insecta [also called class Uniramia] and class Myriopoda), they have jointed legs (four pairs in this case), but they don’t have antennae (insects, millipedes, and centipedes have a single pair). The arachnids are among the most distinctive living invertebrates and have been around for hundreds of millions of years.
Spiders are themselves a group of at least thirty-five thousand species of minute to small invertebrates whose bodies are divided into just two parts: a large cephalothorax or prosoma comprising the head, mouthparts, and eyes, as well as the muscles that work the legs; and a generally rounded abdomen or opisthosoma that contains reproductive organs, breathing organs, the heart, kidneylike organs, and the silk glands, as well as a major part of the digestive organs. The cephalothorax and abdomen are connected by a short, narrow tube—called the pedicel—through which pass the gut, blood sinuses, and nerves. Spiders are found virtually everywhere. There are probably at least a dozen species lurking around your kitchen right now, as well as another fifty species in your flower garden. Arachnologists divide the spiders into about one hundred smaller groups of closely related species; these groups are called families. Of these, about 15 percent comprise the primitive forms known all together as tarantulas and their allies, suborder Mygalomorphae.
Tarantulas overall are medium-sized, generally smooth spiders that have two large, projecting jaws called chelicerae (singular, chelicera), each ending in a slightly curved fang that is used to inject venom into the prey. The fang rotates up and down parallel to the center axis or plane of the body, whereas in most other spiders (advanced spiders, suborder Araneomorphae) the fangs are angled so when opened they are oblique or even perpendicular to the axis of the body. There is some indirect evidence that tarantulas were around as far back as four hundred million years, even before insects learned to fly.
Of the fifteen tarantula families, about half build tubular burrows capped with a door of thickened silk that can be rotated to allow the spider to reach out and grab passing prey. These trapdoor tarantulas often have a row of teeth (the rastellum) on the chelicerae that helps them dig their burrows. Most are small and are seldom seen, though some can be collected in the easternUnited Statesas far north asConnecticut. A few species of the families Ctenizidae and Idiopidae are large enough to interest hobbyists.
The remaining families of tarantulas include generally small, smooth species with a variety of habits, but in the pet trade only the members of the family Theraphosidae (known as theraphosids)—the true or hairy tarantulas or bird spiders—are of great interest to pet keepers. Once called family Avicularidae, these generally are large spiders, commonly 1 1/2 to 4 inches (3.8 to 10 centimeters) long, with projecting chelicerae, a rounded abdomen, and long hairs or bristles of many types on the legs and usually on the abdomen. Most true tarantulas burrow into the substrate or hide during the day under a shelter, but a few species are arboreal (tree-dwelling), building large masses of webs on trees and shrubs. For years literature has said that there are about eight hundred species of true tarantulas, but certainly by now the number must be closer to nine hundred, with perhaps several hundred more still to be defined by scientists. At least one hundred species appear in the hobby on occasion, but only twenty-five or fewer species form the core of the hobby—the species that are readily available to general hobbyists and beginners, that may be somewhat colorful or have distinctive behavior, and that can be kept with relative ease.
Like other spiders, tarantulas have two major body divisions (the anterior cephalothorax, or prosoma, and the posterior abdomen, or opisthosoma) connected by a short stem or pedicel. They also have four pairs of walking legs, each ending in a pair of claws and all originating from the sternum under the cephalothorax. With very few exceptions, all spiders produce venom from long glands in the cephalothorax and/or chelicerae, but most are completely harmless to humans. Let’s take a quick look at some of the more obvious parts of a tarantula’s anatomy, especially the parts used for feeding and identification.