Differences in the occurrence of leg glands between the social parasite S. mutica (Brown, 1949) and other Strumigenys ants

We studied 12 species of Strumigenys and confirmed the existence of class-1 apicofemoral and apicotibial glands as exclusive exocrine structures in workers, queens and males in this ant genus. Contrary to the majority of Strumigenys species, these glands are lacking in workers of S. mutica although they are present in queens. This striking discovery may be related with the social parasitic lifestyle of this species; however, it remains entirely speculative in which way the absence of these glands in workers could be beneficial for their social parasitism. The ultrastructure of the glands displays unique epithelial characteristics which include their bowl shape, the occurrence of a swollen nerve wedged between the gland cells and a complex system of irregular microvilli that are separated from the overlaying cuticle by a cytoplasmic layer. Although the function of the glands is still unknown, their cytoplasmic appearance indicates the production of a possibly pheromonal secretion. In addition to the epithelial apicofemoral and apicotibial glands, we also found class-3 dorsodistal femoral and dorsodistal tibial glands as new structures in the exocrine repertoire of ants. As these glands are also present in S. mutica queens but absent in workers, it is a challenge to further study and understand the social parasitism of this species.