Comparison of foraging tool use in two species of myrmicine ants (Hymenoptera: Formicidae)

The tool-using behavior of Aphaenogaster species has been well studied in
the past few years, however, our knowledge of other myrmicine ants is
rather limited. The aim of the present study was to compare the tool-using
behavior of two closely related myrmicine ants with different feeding
behaviors: Aphaenogaster subterranea, an omnivorous species, and Messor
structor, a mainly granivorous species, which is also known to use tools
when feeding on liquids. We tested the hypothesis that due to the
difference in diet, the tool-using behavior differs in these two species
being more complex and dynamic in A. subterranea than in
M. structor. Consistent with our hypothesis, the foraging workers
of M. structor dropped and retrieved significantly less tools
into/from honey-water baits than A. subterranea, and, contrary to
the latter species, showed no preference towards any specific tools. In
addition, tool dropping was significantly slower in M. structor,
and the dropping and retrieving of tools began significantly later than in
A. subterranea. For seed-harvester ants, the ability to
effectively transport liquid food via tools may not be as significant as
for Aphaenogaster species that regularly utilize and compete for liquid
food sources. Dropping tools into liquids, however, may still be adaptive
for seed-harvester species as a means to supplement diet with liquid food
during periods of seed shortage and also to serve as a defensive behavior
against threatening liquids close to the nest.