Petiole (insect anatomy)
The petiole can consist of either one or two segments, a characteristic that separates major subfamilies of ants.
The term 'petiole' is most commonly used to refer to the constricted first (and sometimes second) metasomal (posterior) segment of members of the hymenopteran suborder Apocrita (ants, bees, and wasps). It is sometimes also used to refer to other insects with similar body shapes, where the metasomal base is constricted. The petiole is occasionally called a pedicel, but in entomology, that term is more correctly reserved for the second segment of the antenna; while in arachnology, 'pedicel' is the accepted term to define the constriction between the cephalothorax and abdomen of spiders.
The structure of the petiole is an easy way to visually classify ants, because the major subfamilies of Formicidae have structural differences: some ants have two-segmented petioles, while others have a single-segmented petiole.
Petiole may also be used in the context of wing veins, where a wing cell that is ordinarily four-sided is reduced to a triangle with a stalk (the cell thus being 'petiolate').
The stalk at the base of paper wasp nests is also called a petiole.