Adventures Among Ants - Mark W. Moffett [96]
that while pupae sink and are often lost during a flood, the larvae float, especially sexual larvae, which are full of bubbles of oil or maybe gas—a product of digestion in a closed one-way digestive tract. If you look at the raft from underneath, you see the larvae being used as inner tubes, held together by the grappling-hooked feet of the workers. On top of the raft, the workers around the edge reach out with their forelegs to grab anything that floats or is anchored. As they reach, other ants walk on top of them, grapple onto them and stretch out over them. So the raft begins to look like an amoeba, with arms of ants extending from the edge in little fingers.
She went on to recount how one of the fingers eventually latches onto a branch or piece of grass, which is followed by a rush to the shore.
In the Amazon basin, seasonal flooding caused by runoff from the Andes drives terrestrial invertebrates into the trees, which serve as a commodious version of Noah’s Ark. Entire ant colonies are among the menagerie ascending the tree trunks, although it’s unclear how all of them find makeshift living space there.26 As conservationist Michael Goulding writes,
At the beginning of the rainy season . . . soil arthropods begin to migrate upwards to the trunk and canopy layers with spiders, millipedes, and centipedes being especially common. Most arthropod groups appear to migrate before the actual inundation starts. . . . [Others,] however, wait it out, and only leave the forest floor when it is flooded. Sow bugs (tiny crustaceans) and small spiders are among these adamant groups. Spiders especially, but also predaceous ants, form a veritable gauntlet that upward-moving, flood-fleeing invertebrates must run.27
Probably most ants can swim to some degree, though to my eye, marauder ants appear to do little more than flail wildly. As the Amazon waters rise, leafcutter workers can walk on the water surface to nearby tree trunks or swim to them when flooding becomes severe. If a worker misses a trunk, she stops swimming and floats along until she passes near another.28 The common carpenter ant of the eastern United States is equally good at swimming. To generate thrust, a worker moves her forelegs in the same manner as she does when walking, while employing her middle and hind legs as a rudder for making turns. For another carpenter ant, the giant Camponotus gigas of Malaysia, swimming, like climbing, is no big deal; instead of detouring, workers paddle across any puddles in their path.29 Indeed, a Camponotus gigas should find it easier to swim than a marauder ant, because water offers more resistance to a smaller individual. However, the marauder will carry more air down with her, proportional to her size, which she can use for breathing and to make herself more buoyant for her slow haul back to shore.
A Camponotus schmitzi worker free-diving into the digestive fluids of a pitcher plant in Brunei, Borneo, where it will retrieve the corpse of a cricket.
In the mangrove swamps of northern Australia lives an ant that swims as a matter of course. Nests of the spiny ant Polyrhachis sokolova can remain underwater for several hours at high tide. As the waters begin to rise, the workers swim on the ocean surface to reach the raised entrance cones in the mud, rowing with their front two pairs of legs and using the back pair as a rudder. Once inundated, the sandy cones collapse, plugging the colony safely inside. If an ant doesn’t get back to the nest in time, she awaits the return of low tide on the trunk of a nearby mangrove tree. When the waters recede, the nests are opened by the ants sealed underground, which then walk out to hunt small crustaceans on the mud flats.30
One plant-dwelling carpenter ant species has incorporated