Adventures Among Ants - Mark W. Moffett [92]
As a tree-climbing biologist, my anxiety that the branch bearing my weight could break is matched only by my fear of confronting bullet ants while high on a rope and unable to flee. Luckily, on that day I was neither on a rope nor high. Letting go of the trunk, I thrust out with my feet and fell the 2 meters to the ground, landing safely away from the bullet ant nest.
For humans, height is significant because we fear a fall. But falling is not the same for every being, as biologist John Haldane describes: “You can drop a mouse down a thousand-yard mine shaft and, on arriving at the bottom, it gets a slight shock and walks away. A rat is killed, a man is broken, and a horse splashes.”5 For animals larger than a mouse, there is a height above which a fall can cause harm; call it the critical-injury height. People come away from the majority of short falls with no more than a bruise, while scampering squirrels plunge meters without injury. But an ant can, in theory, fall forever without being bruised.
The distance covered, however, can have serious implications for ants. The farther a worker drops, the longer she takes to return home, and the more likely it is that she will get lost or die in enemy hands. Perhaps for this reason canopy ants are particularly good at hanging on tight. I made the acquaintance of one such species, Daceton armigerum, while exploring the Orinoco basin of Venezuela. Daceton are unmistakable: big and spiny, with lobes at the back of their head to accommodate muscles that power snap-action mandibles. These ants really knew their place within the forest strata: this colony was nesting 6 meters up a small tree, but the few that descended the trunk avoided the ground altogether, retreating the instant they touched the earth. These same ants had no aversion to walking on a humus-covered branch laden with epiphytes I placed before them. I hadn’t a clue how the Daceton workers recognized the ground, or why they found it so alarming, but for them the forest floor seemed like truly foreign soil. Given this distaste for touching down, it came as no surprise to us that after removing the tree and bisecting its hollow trunk at the village hotel, over the protestations of our maid, we found that each of the 2,342 workers could grip anything—nest, bathroom tile, ceiling—as if her feet were glued in place. I realized then how important clingy feet are to foraging and living in the treetops.
A turtle ant, Cephalotes atratus, gliding backward, toward the left in this image.
Weaver ants show no antipathy for the earth, ranging freely from treetop to ground. For them, a fall has little cost: a plummeting ant will land within her colony borders, with almost no chance of going astray. They still must avoid losing their grip when struggling with enemies and prey, which is why they resemble Daceton in having strong gripping feet. To avoid coming to physical blows, which might lead to tumbles, many arboreal ant species fight at a distance with noxious sprays.6
One way or another, ants do fall, and in such numbers that they can amount to an ant rain. Ground-dwelling European wood ants, Formica aquilonia, which forage in the trees, plummet from the canopy by the millions each day. Formica rain harder, so to speak, when near foraging birds. Some are knocked off branches, but others jump to avoid bird