Army ant ecology

Providing all the same info and more info to boot you can check out the Blog entry at http://pbertner.wordpr​ess.com/heart-of-the-swarm/ or else just read the condensed version here.

Heart of the swarm - within an army ant raid:

Army ant foraging column:

Army ant foraging expedition. Larger prey is carried underneath the abdomen of the ant and may sometimes require the combined efforts of a small legion. This is especially the case in longer, bulkier prey like worms and millipedes.

Army ant soldier:

Ready to bite and brandishing its disproportionately huge mandibles, natives are said to have used the soldiers to suture shut wounds. By pressing the always keen to bite soldiers to edges of the wound the mandibles are used like staples and the bodies simply twisted off, leaving the heads in place.

A routine cleaning:

Army ant soldier having its mandibles cleaned by a minor worker. While standing guard for the column the soldier is treated every once and a while to a cleaning and once over by the smaller minor workers. These smaller ants clamber over the larger ant offering a spot inspection. This is presumably to clear it of any parasites.

Army ants carrying an obligate commensal - An army ant mimicking Staphylinid beetle:

Since the army ant column is in a constant state of motion due to its nomadic nature can be very difficult to determine the nature of the prey captured. Hence I was very fortunate to catch this photo which I only realized afterwards was of a mimic rather than prey larva.

Adult Staphylinid beetle (Obligate army ant commensal):

Finally able to isolate a mimic after several hours of observation the Staphylinid beetle though having some of the morphological traits of an army ant (enlarged gaster (posterior of the abdomen), long legs and small head) the differences become even more apparent upon closer observation. Therefore how does this obvious intruder maintain its facade? It appears that the deception is mostly chemical. Since most ants, and army ants in particular have poor vision they rely chiefly on tactile and chemical cues known as pheromones to communicate with one another. With respect to the former, it has been posited that the sensitive antennae with which ants palpate one another in greeting recognizes distinct morphological traits, building up a ‘mental picture’ to distinguish ‘ant’ from ‘non-ant’. This image is further refined by pheromones. Since each ant colony produces a colony-specific pheromone, these commensals are obliged to live, grow and breed within the colony lest they be perceived as foreigners. Their exclusion from the colony would almost certainly result in death without the protection and abundant source of food provided by the colony.

Dorsal view illustrates a more ant-like form, though the large compound eyes and segmented abdomen as well as the elytra are a giveaway.

An opportunistic tachinid fly:

In addition to the more insidious mimics scrounging off the hard work of the colony there is a litany of followers and commensals. One such class is a variety of flies that follow the army ant column. Seen here perched safely out of reach of a raiding column. This fly takes advantage of all the potential prey insects stirred into a frenzy which accompanies every raid. At times the fly may even make so bold as to snatch dead prey from the jaws of a worker.

Thanks for looking and commenting,
Paul

Though this photo leaves a lot to be desired it highlights the difficulty of framing a moving subject at high magnification. This was the only true 'in situ' shot I managed of the Staphylinid beetle without extracting it from its natural environment ie. the army ant column. The beetle is deceptively small, about the same size as other minor workers. Despite the differences highlighted in the highly magnified view below, one can imagine that in a colony of millions that these insects go unnoticed notwithstanding the scrutiny of a few keen eyed biologists and those who actually go specifically looking for them.
Spoils of raid:



an amblypygid juvenile captured by a worker:

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Army ant mimicking rove beetle:

Another shot that could be improved upon, however, once again the constant motion made it difficult to adequately capture. Once again the differences seem to outweigh the similarities between the rove beetle and its model- the army ant. Interestingly though the beetle will raise the posterior of the abdomen to maximize the apparent size. Apparently in an effort to appear more like the gaster of its model.

Thanks for looking and commenting,
Paul