Ant colonies > Internal structure of ants > Median eyes or stemmata

Median eyes or stemmata

The Median Eyes, or Stemmata

These occur in the males and females of early all ants and in the workers and soldiers of a number of genera. They are largest in the males and always of very small size in the workers. In the male Dorylii, Ecitonii and Ponerinae they are unusually well developed.

In general, it may be said that they tend to vary in correlation with the lateral eyes: the better these are developed, the larger are the stemmata. Structurally the latter cannot be derived from a simple type of sensilla, like that to which we have referred the lateral eyes and the other sense-organs above described. On this account some authors believe that the stemmata are unique and ex­tremely ancient organs, i.e., relicts of eyes that preceded the lateral eyes in the phylogeny of insects.

It should be noted, however, that both lateral eyes and stemmata present the same development in the earliest known fossil insects, the Carboniferous Palaeodictyoptera, that they do in recent species. The stemmata are supposed to give an indistinct visual image of very near objects.