Travel to the Amazon and flick an ant off a leaf, and you might be surprised what you see. Certain rainforest ant species can control their falls and glide back onto the trunks of the trees they came from. Unlike Superman, though, they're only flying to rescue themselves. An ant is light enough that a drop to the forest floor might not hurt it. But the other animals cruising the ground for snacks will cause trouble for that ant soon enough. That's why many rainforest ants have evolved to stretch out their legs and glide to safety after a fall. By staying off the ground, they stay alive a little longer. Yonatan Munk, a researcher at the University of Washington, traveled to Panama and Peru to study one of these ants in particular, called Cephalotes atratus. Munk and his coauthors wanted to see exactly how this gliding ant gets itself back to its home base. He collected wild ants from colonies at both sites (using "a mixture of honey and canned tuna as bait," in case you want to try this at home). Then Munk carried the ants into the treetops. While dangling from a branch in a harness, he gripped each ant gently with forceps. Then he dropped it. An elaborate camera setup let the researchers capture each ant's path in three dimensions as it fell, then digitize its trajectory. They recorded the paths of 58 ants that Munk dropped just one meter from the nearest tree trunk, and another 13 ants that were three meters from the trunk. To stabilize their bodies and start flying, C. atratus ants hold their legs up and out from their bodies. And they actually glide backward, reaching their targets butt-first. The ants have wide heads, Munk explains, and "their eyes are set sufficiently far out that they're able to see behind as well as in front of them." Nearly all the ants that Munk dropped swooped straight to the nearest tree trunk. Five of them targeted a different bit of nearby vegetation instead. Another 11 ants failed on their first attempt at safety, bouncing off the tree trunk. Yet they were usually able to keep gliding and make another landing. The researchers didn't bother recapturing the ants after dropping them—but they did observe many of their subjects marching back up the tree trunk toward the canopy. Digital analysis of the ants' trajectories showed that they were in control of their glides. As each ant fell, its angle of descent grew shallower. And the ants steered their flights, perhaps using the position of their limbs, to reach their targets. In fact, they steered so efficiently that their paths were only one percent longer than a straight line would have been. "The most surprising part of our results," Munk says, "was how little time most ants needed to identify their targets." The researchers had expected that ants wouldn't start steering toward their chosen tree trunks until they hit terminal velocity. But they saw that ants aimed for their landing sites even while their bodies were still accelerating. Munk's coauthor Stephen Yanoviak posted this video of a gliding ant falling toward a tree trunk on his website:
After you watch, you may want to add a new item to your list of heroically soaring objects: It's a bird! It's a plane!...It's a rainforest ant saving its own behind!
Image by Yonatan Munk (via Flickr)
Munk Y, Yanoviak SP, Koehl MA, & Dudley R (2015). The descent of ant: field-measured performance of gliding ants. The Journal of experimental biology PMID: 25788722
