● SW of Pyramid Lake [Washoe Co], NV USA [el. 1323 m / 4341 ft] view location in Google Maps »
● 6/24/10 8:20AM mostly sunny, air temp: 22°C / 72°F
[IMAGE 5 of 5] About two dozen P.occidentalis workers started foraging along an approximately 4.5m / 15 ft long trunk trail , that extended from the nest in a northwesterly direction. Some of them began finding petals from saltbush plants (Atriplex sp.), and carrying them back to the nest from as far away as 3m / 10 feet. [scroll down for additional notes/references]
Pogonomyrmex occidentalis, and P.salinus are generally regarded to be 'trunk-trail foragers'. In many cases, multiple, well established trails lead away from the nest in different directions. Workers travel along these paths to the end, and then disperse, or 'fan out' to search individually for seeds or other food items. After securing something (or in many cases failing to do so), the ants return individually to the nest by way of the trunk trail. In many Pogonomyrmex species, trunk-trails have been shown to be oriented so that foraging ants from neighboring colonies avoid mass confrontations during their searches for food. This allows there to be a greater density of nests in a given area, with minimal conflict.
These trails are initially established (and reinforced) by pheromones laid down by the ants. In at least one species (P. barbatus), foraging workers are influenced in their choice of which of multiple trails to utilize on a given day, by 'patrollers' - workers who leave the nest first in the morning, and scout the area. They then lay a short chemical trail with secretions from the Dufour's gland, from the nest entrance to the start of a particular trunk-trail(s). Evidence suggests that the direction chosen by the patrollers is not so much based on food availability, but by their encounters with patrollers from neighboring colonies.
The visibility and length of trunk-trails can vary greatly. The P.salinus trails we have observed so far (in Oregon and Washington states), while occasionally very visible (and free of vegetation), are more often indistinct, and not easily observable unless ants are traveling along them. As mentioned elsewhere on this site, we have observed trunk-trails of Pogonomyrmex salinus 9m / 29.5ft or more in length - though it is our experience that they are usually much shorter - and many nests (the majority in some locations) have no visible trails.
We also observe these ants foraging individually near the nest, in Oregon and Washington states.
·Greene, M.J. & D.M. Gordon. 2007. How Patrollers Set Foraging Direction in Harvester Ants. The American Naturalist, Vol. 170, No. 6, December 2007
·Hölldobler, B.1974. Home Range Orientation and Territoriality in Harvesting Ants. Proceedings of the National Academy of Sciences USA, Vol. 71, No. 8, pp. 3274-3277, August 1974
·Hölldobler, B. & E.O. Wilson.1990. The Ants. Cambridge, MA, Belknap/Harvard Press
·Johnson, R.A. 2000. Seed Harvesting Ants (Hymenoptera: Formicidae) of North America: An Overview of Ecology and Biogeography. Sociobiology Vol.36, No. 1, 2000
·Jorgensen C.D. & Porter, S.D. 1982. Foraging Behavior of Pogonomyrmex Owyheei in Southeast Idaho. Environmental Entomology, Vol. 11, No. 2, April 1982
- Pogolumina - Pogonomyrmex Harvester Ants of North America
These images depict Pogonomyrmex occidentails
workers in the state of Nevada, USA. This is the well known 'western harvester ant'. Scroll down PAST BOTTOM OF PAGE for complete image description, and CLICK large image to make it even LARGER...