Carpenter ants follow trails. Just watch them wandering about on your wooden porch until they strike a trail of pheromones (chemicals ants use for communication) that another ant has laid down.
Ants don’t have noses, so they wave their antennas around to pick up the trail, then off they go on the road to ruin. (Carpenter ants destroy houses.)
Scientists know plenty about ants, including their ability to follow scent trails, but researchers at Harvard wanted to get a more detailed understanding of how exactly ants sniff, or taste, the pheromone-marked path.
First, some basics: Ants use their antennas to pick up chemical cues left by other ants.
And the chemical sense of ants, call it smell or taste or chemo-reception, enables them to follow straight trails, curved trails, even zigzags.
To see how ants do it, the scientists mixed ink and ant pheromones and used the result to paint trails on paper.
They set ants out on trails and recorded dozens of hours of ant movement. They analyzed the video and tried out different computer models of the ants’ behavior.
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What Ryan W. Draft and his adviser, Venkatesh N. Murthy, and other researchers found was that the ants had several strategies for path-following. The scientists published their results in the Journal of Experimental Biology.
All the ants used their antennas to sweep the trail side to side. One strategy they used was probing. A probing ant moved slowly, keeping its antennas close together.
The researchers termed another strategy exploratory: Ants still moved slowly, but they took winding paths moving away from and back to a trail.
When they were locked into a pheromone trail, they moved along more quickly, keeping their antennas on either side of the path. They kept one antenna closer to the path, but which antenna varied from ant to ant. In other words, some were lefties and others were righties.
Also, despite the reputation that ants have in fables as industrious, some ants were more persistent than others. The idea that ants are all hard-wired robots that do the same thing just didn’t apply.
An understanding of their behavior could, however, be useful in building just such robots.
Dr. Murthy views the successes of this experiment as an indication that the researchers have found a good method for studying ant navigation in detail. “I think we were humbled by the ants and seeing just how sophisticated their behaviors are,” he said. “Humbled, but not discouraged.”
