The nests of many Pogonomyrmex ants (e.g. Pogonomyrmex salinus & P. occidentalis) often undergo distinct and predictable changes in their external structure, over time. A typical sequence in the developmental stages of the visible (above ground) portion of a P. salinus nest, could be as follows: [be sure to scroll down below bottom of page for complete description]

[A] The incipient nest begins when a queen mates, sheds her wings, and tunnels down at an angle into the sand - founding a new colony. A raised crescent of sand remains from the queen's digging activities. When the first workers appear (in many cases, the following Spring), they begin to excavate sand as they create the tunnels, galleries, and chambers that comprise the subterranean portions of the nest. [A: approx. 6.3 cm/2.5 inches diam.]

[B] Gradually, a small crater-like structure forms, consisting mostly of sand - up to this point, it can still be called an incipient nest. At this stage, the workers (who are often smaller than 'normal' Pogo workers, and referred to as nanitic) also begin to remove grass and other plants from the nest vicinity. By doing this, they deprive predators (like spiders) of a convenient and relatively safe place from which to prey upon the ants. Sunlight may also be blocked by plants growing too close to the nest, and roots can damage the tunnels and chambers below. [B: approx. 10 cm/4 inches diam.]

[C] As time passes, the crater may be enlarged greatly as more and more soil is brought up from the depths of the nest. Often, the ants begin to cover the nest structure with uniformly sized gravel pebbles, if they are available in the habitat. At this point, tunnels and galleries may also begin to be constructed inside the crater structure itself. As can be seen in this image (C), the nests are often surrounded by discarded seed capsules and other by-products of the ants' seed harvesting activities. [C: approx. 28 cm/11 inches diam.]

[D] If the conditions are favorable, the external nest structure may attain the form of a symmetrical cone, or dome. If you go back to image C, you will notice that the left side of the crater wall is wider. The ants will slowly build this wider section up until it begins to take the form of a cone. The entrance is displaced toward to the edge of the structure during this process. The final result is often a very large conical mound (or more rounded dome), filled with its own network of tunnels and chambers. It could take 2, 3, or 4 seasons to reach this stage. A colony may inhabit the same nest for 20 years or more, i.e. for the life span of its queen. [D: approx. 39 cm/1.3 feet diam.]

[E] Images A through D show different P. salinus nests at various stages in their 'evolution', to illustrate the various forms an individual nest could take over time. In the real world, however, things sometimes don't work out this way. Strong winds at certain locations can prevent mature colonies from ever developing a nest cone like the kind seen in image D. Very often the nests take the form of a flattened disc (image E). A wide variety of other nest structures will be encountered as well, including multiple nests, nests with no discernable mound structure at all, and nests built so as to incorporate large rocks, or boulders.

It should be noted as well, that the descriptions on this page apply to certain Pogo species only. Many species do not construct cones, domes, or craters like the ones shown above. Also, in keeping with their general variability, these nests can contain one, or many entrance holes.

REFERENCES FOR ENTIRE PAGE:

·Cole, A.C. 1932e. The Rebuilding of Mounds of the Ant, Pogonomyrmex occidentalis, CRESS. Ohio Journal of Science, v32, n3 (May, 1932) 245-246
·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