Psammophore of Pogonomyrmex salinus worker.

Psammophore means 'sand carrying' in Greek. The name Pogonomyrmex itself (also from the Greek) is a reference to this structure - Pogonomyrmex means 'bearded ant'.

The psammophore consists of long curved hairs extending from the ventral surface (underside) of the head that collectively form a basket-like structure that is used to carry loose sand.

The individual hairs that make up the psammophore are called ammochaetae, and the number of these hairs varies among species. As an example, in P. occidentalis, there are 46 ammochaetae on the ventral surface of the head. Other ammochaetae are also present on the mandibles ('jaws') and clypeus (area just above the mandibles when viewing an ant 'head on'). These additional hairs help retain the sand, and prevent it from spilling out (upward/forward) from between the mandibles. It is also very likely that these hairs provide a sensory function during sand-loading, and carrying.

The psammophore can increase the dry-sand-carrying capability of these ants by up to 200%. This advantage seems to apply only to dry sand, however. Damp or wet sand is already easily transportable, and the presence of the psammophore apparently provides little, or no additional benefit. In the wild, Pogos usually [1] don't utilize their psammophores for the transportation of seeds - though they have done so in controlled laboratory experiments, when offered small seeds in very high densities.

Many other 'desert ants' posses psammophores as well, including species of Messor, Pheidole, Myrmecosystus, and others.

[IMAGE: Pogonomyrmex salinus worker specimen from central Oregon (LOC 050), with arrows indicating psammophore] [scroll down for additional notes/references]

[1]
On 6/22/10, we observed and imaged Pogonomyrmex californicus workers carrying multiple small seeds - and using their psammophores in conjunction with their mandibles to achieve this. This is the only time we have seen this. Images and further explanation can be found in the Pogonomyrmex californicus gallery.

References for entire page :

·Fisher, B.L. & S.P. Cover. 2007. Ants of North America: A Guide to the Genera. Berkeley and Los Angeles, CA, University of California Press
·Porter, S.D., and C.D. Jorgensen. 1990. Psammophores: Do Harvester Ants (Hymenoptera: Formicidae) Use These Pouches to Transport Seeds? Journal of the Kansas Entomological Society. 63(1) 138 -149
·Wheeler, W.M. 1907. On Certain Modified Hairs Peculiar to the Ants of Arid Regions