Occupation of twigs by ants in the leaf litter: is there a relationship between the morphology of the castes and the entrance hole?

Fallen twigs on forest floors are an important nesting resource for ants. Despite their abundance in the leaf litter, these twigs are not always colonized, since various attributes affect their occupancy. However, the morphological parameters of ants are potentially linked to the entrance hole size in arboreal species, which will vary among castes. We therefore tested for the relation between the ant morphological traits of different castes and the size of entrance holes in twigs, using communities collected in the leaf litter in areas of the Brazilian Atlantic Forest. We measured a total of 4,159 ant individuals across 60 species and their female castes, and dissected 4,805 twigs, of which 1,064 had entrance holes, 519 hosted ants. The entrance hole size of twigs was also measured. We observed average ant morphological traits (per colony or species level) were positively related to the average size of the entrance holes in the twigs. At the colony level, all five morphological variables measured (head width, head length, scape length, Weber's length, and hind femur length) were related to the entrance hole size in workers and majors, and the same was true for queens except for scape length. At the species level, this pattern was maintained for workers and queens, but in majors hole sizes were only related to their head width. We conclude that the size of the entrance hole is a relevant variable for the occupancy of twigs in the leaf litter by morphologically variable species of twig-nesting ants.