tarsus, tarsi, tarsomere, tarsal formula

From Greek, tarsos, sole of the foot (1).

tarsus noun, plural tarsi, adjective tarsal - the "foot" or last part of the insect leg. It typically has five joints, or segments, called tarsomeres. (Sometimes the number is reduced, and this can be a useful identification aid, e.g., in many beetles.) The tip of the last segment often has tarsal claws, and sometimes there is a pad of hairs underneath these, called a pulvillus (plural pulvilli).

See diagram of insect and spider legs above.

Photos illustrating tarsi:

Tarsal formula refers to the number of tarsomeres on the front, mid and hind legs e.g. "Scarab" Beetles have a tarsal formula of 5-5-5 or 5 tarsomeres on the front legs, 5 on the middle ...

This character is especially useful at family rank and higher.