Allomerus Decemarticulatus - Predatory Behavior

Predatory Behavior

Normally, there are only a small number of ants in any given area on the plant stem. There are about 40 workers per leaf, but only around two will be patrolling outside. Once an insect lands on the plant, the closest ant will immediately surface and grab on to a leg, antenna, wing, or some other appendage of the prey. This ant will pull the prey, which will in return try to escape by pulling the opposite direction. However, the ant will rarely ever let go of its grip. The ant immobilizes the prey and, using an extreme feat of strength, will hold the much larger prey to the plant as more ants from around that area arrive. This ability to hold the prey is extremely important because the ants move and congregate fairly slowly.

After the first ant has immobilized the prey, it releases pheromones to call other ants to the area. The first few ants to arrive will each grab a different leg and pull in opposite directions, "spread-eagling" the prey. This is basically identical to the medieval torture tactic of "rack torture." Anywhere between six and 16 ants will participate in this spread-eagling. As the prey lies motionless and helpless, worker ants will congregate and help either hold the prey down further if that is necessary or start stinging and biting the prey. In doing this, they use a venom that they produce to paralyze and kill the prey. Afterwards, the group of workers will carry the body back to the colony, where it is dismembered and cut up into little pieces to be eaten by the group.

This amazingly gruesome predatory behavior is a great example of a collaboration between solitary and cooperative predation. The first ant will initially act alone in his predation, but after that ant is holding the prey, other ants will come join him in the hunt, and still other ants will travel back to the domatia and recruit even more ants to aid in holding down and eventually dismembering the prey. This also demonstrates how much more effective a group of individuals can be than an individual working on its own. A single ant could never be able to kill such large prey; they are only able to do so by incorporating communication and cooperation.

This predatory behavior is very effective against such large prey that the ants consume. Dejean and other researchers (2001) tested the limits of its effectiveness by exposing the ants to termites and grasshoppers, which are about 40 and 142.2 times the size of the worker ants, respectively. So a single Allomerus decemarticulatus worker restraining a grasshopper is about the equivalence of a 175 pound person holding down a struggling 25,000 pound object that is actively trying to escape. When the termites were exposed, each was captured by the ants; none got away. However, with grasshoppers, all were seized by at least one leg, but out of the 20 introduced, five were captured completely, 12 escaped but lost their leg that was clasped on to by the worker, and seven jumped away.

Any prey that has the ability to jump or fly away will always be more effective in escaping than non-flying insects like the termites. However, many times those that do escape will still lose a leg or other appendage in the process, like 60% of the grasshoppers in this experiment. Because the prey is so much larger than the ants, even just getting this one appendage as a food source is a victory. For example, a hind leg of a grasshopper is still about 12.4 times the size of a single ant and a great resource in itself.