Spider identification

Spines, setae, and hairs

There are a variety of thin, tapered structures that cover the legs of spiders. The smallest ones are fine hairs which are also called setae (singular: seta). Thicker structures are called spines. Some spiders have only fine setae covering their legs, some have both setae and robust spines. Some of the smaller spiders have spines that are so fine that they fall in the gray zone and could qualify for either. Typically, each spine is housed in a socket that looks like a circle around the base of the spine. If the spine is knocked off, the spine socket is still visible and looks like a crater. Therefore, it is easy to determine whether a leg had spines or not, even if no spines are present.

The key uses spination patterns on the tibia of the first leg to differentiate among the species. This is designated as Tibia I spination. The positions of the spines are labeled as dorsal, lateral, ventral, and medial (see below). Some spiders have no spines at all, while some spiders have all four surfaces bearing spines. In some cases, the spine may be at the border of two surfaces, and it will be difficult to assign it to one location or the other. In those cases, the key should be set up to accept both answers, so do not be overly concerned. The key will probably work most reliably for spiders with no spines, with spines on only one surface, or spines on all four surfaces. For some species, spines become more numerous as the spider matures. Therefore, the spination portion of the key should work well for adults but may not be as useful for immatures, since most of the spiders available for examination in building the key were matures. Typically, arachnologists do not save immatures in museum collections because they do not offer much definitive information for species determination.

tibia I illustration tibia I photo