Let Me antertain you
If our house ever catches fire, the cause will undoubtedly be ant-related. Our place is infested by ants. In summer they become so abundant you can't stand in one spot in the garden for long before they are crawling up your legs and sampling your flesh. When an electrician unscrewed a malfunctioning power point recently he was amazed to find that the acid from frazzled ants had eaten away the plastic switch mechanism. During winter months, the first thing I have to do every morning in my office is to switch off the power supply and clean the heater thermostat of corpses of ants that crawled out of the wall cavity during the night and stumbled onto the trigger mechanism, short circuiting it.
When I observed piles of ants forming on the carpet in my office, I thought I'd find out a little more about this habit. I emailed an ant lover friend from the local field naturalists club who lives in a real bush house nearby to ask if she had observed this behavior, too. She replied, “My ants (Polyrhachis) just drop everything below their ceiling nests — of which there are many!” They crawl out on the beams overhead and drop their payloads at random. A little further research revealed that many ant species have a penchant for removing the corpses of dead ants from their nests and dumping them randomly on the ground outside. Then, other ants going about their business above-ground pick up the corpses and stack them in piles. To God must go the credit for all nature's phenomena, even the behavior of “brainless” midgets. What's going on here? We can intuitively appreciate the value to ants of removing smelly dead brethren from their nests, but why dump them in ordered piles? What practical benefit does this behavior confer upon ant colonies?
As to the first question, serious scientists have studied ant piles and come to an interesting conclusion. In their paper, “Spatial patterns in ant colonies” (Proceedings of the National Academy of Sciences USA, published online Jul 11, 2002) Guy Theraulaz et al report that spatial patterns in ant cemeteries result from “local activation and long-range inhibition” processes (LALI processes). They set up a circular “arena” above an ant nest, deposited ant bodies evenly around the edge of the arena then filmed the ants at work, recording their movements on a computer "as a series of X-Y Cartesian |
coordinates”. They describe what happened:
After having reached the arena, workers pick up corpses and drop them to form piles. After a few hours, several clusters are formed. Over time, some clusters grow and others disappear, leading to an apparent steady state with a stable number of clusters… (p. 9646).
As a result of their observations they were able to develop a mathematical model showing that these patterns form as the inevitable result of two instinctive behaviors. First, when an ant is wandering around outside and comes across a lone corpse, it picks it up and carries it around. Second, when a corpse-carrying ant stumbles upon two or more dead ants lying next to each other, it adds its load to the “pile”. These behaviors automatically result in large areas being swept clear of corpses and the formation of local piles.
Now I hate to throw the cat among the pigeons, and wouldn't dream of questioning such research. But I am convinced their explanation does not fully explain my own observations. In my office, corpses are not arranged in piles randomly around the carpet but are almost always found in depressions in the carpet. Where, for example, legs of tables depress the carpet, there the ants lay their dead to rest. On one occasion, they piled them up in a long line directly below one of the computer cables lying about an inch above the carpet. Also, since embarking on the broadband adventure, I have noticed them consistently piling up their dead in front of the little green lights on the modem (see picture below). When I vacuumed up the pile, within a week it was back again on the light-carrying side of the modem. In short, there's more to the marvel of ant piles than mathematics.
We asked above what benefit such behavior could confer on ants. I have not found any suggestions as to how the piling up of corpses in orderly concentrations aboveground could aid and abet the survival or health of the colony down below. In short, how can natural selection explain the development of instinctive behavior that seems to confer no benefit? Could it be that God just wanted to antertain us? |
