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NOV. 5, 2013

The Ant and the Spider, Part 1

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Ants are pretty particular folk. They make it their business to know their neighborhood. When a scout comes back with the latest pheromone news about a stranger on the block or a new deli down the street, it’s only a matter of minutes before the entire colony is gossiping about it. That’s one of the advantages of what the Harvard myrmecologist E.O. Wilson called a “superorganism.” So to walk through a colony’s turf unmolested, uneaten, or ignored is a trick. I stumbled on one of those co-evolutionary strategies at our canoe lake last week when I noticed some black ant scouts doing their usual mad dashing about checking for invaders or snacks. When one of them finally took a breather and sat still for a moment I quickly snapped a photo of this really tiny ant in order to try to identify it later. But when I enlarged the image on my camera I noticed there was something different about this one. It had a small white band around its abdomen and the telltale two-pronged spinnerets of a spider at the back end. But what first threw me was its behavior. Spiders don’t run constantly like ants. Generally, they are sit-and-wait stalkers. Even little kids notice this difference between spiders and ants. This particular coevolution was, in part, a visual mimicry and an effective one, but adding the frantic dashing had convinced me that this was yet another ant. Most importantly, the ants ignored this spider.

Ant mimic spider

This evolutionary track can get quite specific and complex. Some ant symbionts use chemical mimicry to deceive ants, producing pheromones that essentially say “I am an ant, not a predatory beetle.” After the ants search them at their security checkpoints, the predator goes on to ravage the eggs and larvae without challenge.

I don’t know if my spider’s mimicry was a ruse to prey on ants or their larvae or just a way to pass through the neighborhood undetected, Jedi-like, with a wave of a pedipalp (“These are not the droids you’re looking for…”) But after watching for 30 minutes, I suspected this ant-mimic spider was doing just that, passing through a remote, tiny, busy corner of the universe, going about his business unnoticed and completely unaware that he looked just like an ant to the rest of the aliens at the cantina.