● Wanapum Rec. Area [Kittitas Co], WA USA [el. 190 m / 623 ft] view location in Google Maps »
● 5/16/10 9:02AM partly cloudy, air temp: 23°C / 73°F
[IMAGE 2 of 6] Winter rains had apparently washed away most of the external nest mound of this Pogonomyrmex salinus colony, in central Washington state. In addition, large, jagged pebbles were either exposed by the erosion, or deposited around the nest entrance by the flowing water. In this series of images, dozens of workers can be seen attempting to remove the relatively huge rocks, by grasping them with their mandibles and dragging them away. Some of the objects appeared to be too large and heavy to be moved by a single ant, so in some instances, two or more workers would cooperatively carry them. It was also clear that the ants were completely unable to move some of the largest pebbles. Having a jumble of 'boulders' at the entrance to their nest would generally be unacceptable to these ants. The many nooks and crannies would make entering and exiting the nest very difficult (especially while carrying foraged seeds, etc), and spiders and other predators would be provided with many hiding places from which to prey upon colony members. In a situation like this, Pogos may sometimes choose to construct another nest entrance in a more suitable location.
Many Pogo nests sport a prominent gravel-covered mound, cone, or crater which contains a small network of galleries and tunnels. In some cases, this mound feature is not present, and the external nest structure consists simply of entrance holes in the ground, often surrounded by a gravel 'disc', and located within an area cleared of vegetation.
However, like the proverbial 'tip of the iceberg', the above-ground portion of a Pogo nest represents only a tiny fraction of the whole colony - in terms of ant population, and in the physical structure and extent of the nest itself.
The subterranean portions of Pogonomyrmex nests usually contain one or more large (approximately vertical) tunnels - and branching off from these, many 'side burrows' and chambers. These offshoots are more numerous (and larger) nearer the surface, and dwindle in frequency and size, as depth increases. These chambers function as granaries, nurseries, general quarters, and sometimes refuse dumps.
Pogonomyrmex nests can reach considerable depths. Nests of P. rugosus (the rough harvester) have been shown to extend 4 m / 13 ft into the ground, and those of P.occidentalis have been recorded to reach depths of 3 m / 10 ft.
Along with distinct variations among different Pogo species, there are many variables that affect the proportions of a particular colony's nest. It's likely that most nests are somewhat shallower than the figures given above.
·MacKay, W.P. 1981. A Comparison of Nest Phenologies of Three Species of Pogonomyrmex Harvester Ants (Hymenoptera: Formicidae). Psyche, Vol. 88, No. 1-2, 1981
·Taber, S.W. 1998. The World of the Harvester Ants. College Station, TX, Texas A&M University Press.
·Wheeler, W.M. 1910. Ants: Their Structure, Development and Behavior. New York, Columbia University Press
- Pogolumina - Pogonomyrmex Harvester Ants of North America
Images of Pogonomyrmex salinus - at various locations in Nevada, Oregon, and Washington states, USA. Scroll down PAST BOTTOM OF PAGE for complete image description, and CLICK large image to make it even LARGER...
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