Friday, December 02, 2011

The ants shall inherit the earth

Humans are not the dominant species on this planet. Neither is the domestic house cat, though one might be forgiven for drawing that conclusion. No, that honor belongs to the Argentine ants. We were invaded by the very ironically named Linepithema humile last night, and the ensuing battle lasted well over an hour as we vacuumed, sprayed, swept and wiped the little critters from nooks, crannies, cat food dishes and trash cans. (Thank God they had not yet discovered the pantry.)

If ever you need proof that cooperation and altruism can evolve through Darwinian evolution you need look no further. The Argentine ant is one of the most successful species on the planet. But why? They have neither brains nor brawn, no armor, no sting, no bite. They are in fact, if you look at an individual ant, one of the most innocuous creatures you could ever hope to encounter. They're disarmingly unthreatening, almost cute. And if you want to dispatch one you can just squish it like, well, a bug.

But considering an ant as an individual entity is a serious mistake, every bit as wrong as considering one of your white blood cells to be an individual. Notwithstanding that they are not mechanically connected to each other the way the parts of your body are, ants are in fact just components of a fundamentally different, much larger, and far more intimidating whole, the ant colony. Kill an individual ant, or even slaughter them wholesale, and the colony goes on.

So what makes the Argentine ant so singularly threatening among all the species of colony-forming insects in the world? It is that Argentine ant colonies are structured in a fundamentally different way than all of the others. Nearly all other insect colonies are organized around a single individual insect who lays all the eggs. We normally call this insect the "queen" but a more accurate description would be an ovary. This individual or organ, depending on how you choose to look at it, is the colony's soft spot, its Achilles heel. Kill the queen and you kill the colony.

In addition, most insect colonies have a sense of identity based on their genetic identity (since all the individuals in the colony have the same mother). So while the individual ants in a colony will cooperate like the cells in your body, individual colonies will compete with each other for food and territory.

Argentine ants aren't like that. A single colony can have multiple queens, and when Argentine ant colonies encounter each other, they don't fight. It's as if all of the Argentine ant colonies on the entire planet have drawn up a mutual cooperation treaty. An individual ant is a member not just of a colony, but of a planet-wide super colony. This makes Argentine ants virtually impossible to eradicate without sterilizing the entire planet.

To battle an Argentine ant invasion it is not enough therefore to simply kill the ants that you see, because there's almost certainly an effectively infinite supply of them hidden away at the other end of their trail. The only effective defense against them is to infiltrate the colony with poison-laced food, which takes several days to be effective. Happily, but ominously, in our case we were able to track the infestation back to its source, which turned out to be a potted fern in our dining room. It was happy because we were able to just take the fern outside and dispense with the multi-day poisoning operation. But it was ominous because we have no freakin' clue how that colony came to become established there in the first place. That fern has been sitting in our dining room on a three-leged metal stand for months and months. We water it regularly. Until last night we never saw even a single ant there.

Kinda creepy.


coby said...

Interesting bit of ant trivia: There are more ants on this planet than there are weight!

Anonymous said...

In my experience (in a previously owned Eichler house), it is sufficient to divert Argentine ant trail(s) to outdoors -- rather than trying to eliminate the colony. It sounds as though this is effectively what Ron did by removing the potted fern.