The median line, posterior to this area, often shows a groove called the frontal groove. The degree of clypeus development varies among genera. It is extremely small in the genus Odontomachus. The shape of the anterior margin of the clypeus is sometimes important when distinguishing among different genera. The degree of eye development is variable.
Some ants have an eye composed of only one facet.
There are some ants which have no eye. The location and degree of development of eyes are taxonomically important. Workers often have no ocellus. The antenna of the worker and the female is usually composed of 12 segments, while that of the male is often composed of 13 segments. The number of segments is smaller in some genera.