Sternal glands in Strumigenys ants

Strumigenys ants are characterized by an extraordinary developed exocrine system with 10 glands exclusively found in this genus. Making a survey of 18 species, we discovered two additional glands in workers and queens that are located underneath the anterior third of the 6th and 7th sternites. The epithelial glands are formed by cubic to cylindrical cells that have tortuous lateral cell membranes with interdigitations and apical septate junctions, smooth endoplasmic reticulum and apical microvilli. The glands occur in near proximity to the sting base and therefore may display fortifications to protect them against the sting movements during its extrusion and retraction. The external cuticle that covers the gland region displays small transverse grooves and transcuticular channels. The most developed glands were found in workers of the social parasite Strumigenys mutica, although the eventual link with social parasitism remains unclear. In workers of S. sauteri the glands are rudimentary or absent which may be related with prey capture in this species that occurs without use of the sting. Whereas sternal glands in other ants often produce trail pheromones, this role can be excluded in Strumigenys as trail following does not occur in this genus.