The Florida Harvester Ant, Pogonomyrmex badius, Relies on Germination to Consume Large Seeds

Abstract

The Florida harvester ant, Pogonomyrmex badius, is one of many ant species and genera that stores large numbers of seeds in damp, underground chambers for later consumption. A comparison of the sizes of seeds recovered from storage chambers with those of seed husks discarded following consumption revealed that the used seeds are far smaller than stored seeds. This difference in use-rate was confirmed in field and laboratory colonies by offering marked seeds of various sizes and monitoring the appearance of size-specific chaff. Because foragers collect a range of seed sizes but only open small seeds, large seeds accumulate, forming 70% or more of the weight of seed stores. Major workers increase the rates at which small and medium seeds are opened, but do not increase the size range of opened seeds. Experiments limiting ant access to portions of natural seed chambers showed that seeds germinate during storage, but that the ants rapidly remove them. When offered alongside non germinating seeds, germinating seeds were preferentially fed to larvae. The rate of germination during the annual cycle was determined by both burial in artificial chambers at various depths and under four laboratory temperatures. The germination rate depends upon the species of seed, the soil/laboratory temperature and/or the elapsed time. The seasonal soil temperature cycle generated germination patterns that vary with the mix of locally-available seeds. Taken together, exploitation of germination greatly increases the resources available to the ants in space and time. While the largest seeds may have the nutritional value of 15 small seeds, the inability of workers to open large seeds at will precludes them from rapid use during catastrophic events. The harvester ant’s approach to seed harvesting is therefore two-pronged, with both immediate and delayed payoffs arising from the tendency to forage for a wide variety of seeds sizes.

An illustrated guide to seeds found in nests of the Florida harvester ant, Pogonomyrmex badius

“…Four size classes of the 2014 seeds were used in a series of experiments on the consumption of germinating and non-germinating seeds. The results of these studies can be found in Tschinkel and Kwapich [ 21 ].…”

“…Although early observers sometimes noted germinating seeds in the nests of harvesting ants, the possibility that the ants might actually require some seeds to germinate in order to be able to eat them was never carefully investigated until the recent work of Tschinkel and Kwapich [ 21 ]. Through experiments and observations, Tschinkel and Kwapich [ 21 ] showed that P .…”

“…Although early observers sometimes noted germinating seeds in the nests of harvesting ants, the possibility that the ants might actually require some seeds to germinate in order to be able to eat them was never carefully investigated until the recent work of Tschinkel and Kwapich [ 21 ]. Through experiments and observations, Tschinkel and Kwapich [ 21 ] showed that P . badius workers cannot open seeds larger than 1 to 1.4 mm wide, that they readily use germinated seeds, feeding these to larvae, that seeds actually germinate within the subterranean storage chamber are rapidly removed by workers to be fed to larvae, and that seed germination rates are related to the seed species, the season and temperature.…”

“…This paper is a companion paper to that of Tschinkel and Kwapich [ 21 ] for the purpose of providing identifications and images of the 58 species of seeds taken from P . badius nests.…”

Evaluation of Spent Engine Oil and other Natural Materials on the Emergence of Harvester Ants (Messor galla Forel) in North Eastern Nigeria

“…Cereal grains like Millet, Wheat, Sorghum and Rice are major staple foods and raw materials in bakeries and brewing industries which have been reported to be ravaged by the activities of harvester ants (Nicola et al, 2013). As a field and store pest, the harvester ant causes extensive damage and losses by foraging on sown seeds, sometimes feeding on germinated crops and also climbing some plants to harvest matured seeds/grains (Heathwole, 1996;Tschinkel and Kwapich, 2016). They also reduce plant stands by denudation of cultivated lands as they destroy the plants around the entrance to their nest leading to bare patches in the fields measuring several square metres.…”