Identifying tarantulas is seldom straightforward; however, as the common species become more readily available as captive-bred specimens, there is less variation to be expected in a single species. Look first at the general appearance of the spider.
Is it exceptionally hairy or smooth? Is one pair of legs much longer or heavier than the others? Is there a horn or tubercle on the carapace? Is there an obvious color pattern on the carapace or abdomen? For that matter, is there a , strong color pattern on the legs, and if so which segments of the leg have the color? Is the red ring on the patella (knee) or on the top of the tibia? Though many tarantulas are shades of brown and black, a surprising number of the most commonly kept species have distinctive and constant color patterns that are easy to learn and remember.
To a specialist, most of the features mentioned above are just secondary. What counts are details of structure. Are there thick-based bristles at the sides of the chelicerae, pedipalps, or first walking legs? For that matter, are there long or strongly modified bristles on any part of the body? Are there teeth on the chelicerae other than the fangs? Is the foveal groove straight or curved? Are there secondary grooves on the cephalothorax? If you look closely (with a microscope or strong magnifying loupe), are there special pads of bristles (scopulae) under the first two segments of the legs that help the tarantula climb? What is the detailed structure of the sperm bulb and its point (embolus), as well as the projecting part of the tarsus above it? In a female, what is the structure of spermathecae extending from the epigastric furrow that are used to store sperm?
It also is important to know where a tarantula originally came from. A surprising number of unrelated tarantulas from theAmericasandAsia, for instance, look much alike at first and even second glance. Sometimes even behavior can be a useful feature: American tarantulas often have nearly bare upper abdomens because they have scraped off the urticating bristles; African and Asian tarantulas lack these bristles and thus shouldn’t have a bare patch on the abdomen.
All tarantulas that have been described by scientists carry scientific names, which are written in italics to set them off from surrounding text. These names all are based on Latin, Greek, or at least Latinized words from other languages. A complete scientific name consists of the genus (plural, genera) written as a capitalized word (equivalent to a last or family name for humans) and a specific name—the species (species is both singular and plural)—that is never capitalized. The specific name is similar to your first or given name. Therefore, the name Joe Doe as a scientific name might be given as Doeus josephus. Often the scientific name is accompanied by the name of the scientist who described the species and the date: Aphonopelma hentzi (Girard 1854). When the describer’s name is in parentheses, it indicates the species was originally described in a different genus—a very common case in tarantulas.
What is a species? Opinions vary among scientists and hobbyists. As a general rule, a species can be a group of populations that share a similar appearance and can freely breed with one another in nature to produce fertile offspring that resemble the parents.
Species have a distinct range, usually defined by geographical or ecological barriers, but two very similar species may occupy the same range when separated by behavioral or physiological differences that prevent successful interbreeding (hybridization). A subspecies is a group of populations within the range of a species that differs in some detail of features yet is capable of breeding successfully with other populations of the species. Two subspecies cannot occupy the same range, as they would continually interbreed to produce intermediate offspring that would not have the characters of the parents.