Archetype

Homology Weekly: Petiole, Postpetiole and “Tubulation”

An isolated second abdominal segment constitutes the characteristic petiole (blue) in ants. Pachycondyla stigma worker (Scanning Electron Micrograph, Roberto Keller/AMNH)

The easiest way to know you are looking at an ant is to pay attention to its waist: if it consists of one or two nicely isolated segments you can be sure you made a positive identification. The basal condition for the family, common to all ants, is to have the second abdominal segment in the shape of a node or scale and distinctly isolated from the rest of the abdomen to form a petiole (remember that the first abdominal segment is coupled to the thorax as the propodeum). The functional advantage of such novel architecture seems to be an enhanced articulation between body segments, and thus greater mobility for a posterior part of the body that bears the ant’s weapons in the form of a sting or other specialized chemical producing  organs like the acidopore.¹
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Tags: Adetomyrma, Dorylus, Homeosis, Leptanilloides, Petiole, Postpetiole, Postsclerite, Presclerite, Sphictomyrmex