Adventures Among Ants - Mark W. Moffett [97]
A pitcher plant is not ordinarily a healthy place for an ant, since these plants are carnivorous. A cup that grows from the twisted tendril at the end of each of their modified leaves holds a liquid into which insects tumble and drown after “aquaplaning” over the pitcher’s slick rim much as a man slips on a banana peel.32 The plant secretes digestive enzymes into this liquid that break down the corpses and help the pitcher absorb their nutrients. Ants are the plant’s most common meal, except for the resident species of carpenter ant, Camponotus schmitzi, which nests in the pitchers’ tendrils and takes dips in the liquid, emerging alive and well.
That afternoon, I watched ants dive into the cups for a swim, staying underwater for up to thirty seconds. At the floor of one pool, two workers tugged at the corpse of a cricket, dragging it up through the water meniscus—a feat in itself, given how difficult it is for a small being to break the surface tension in a body of water. Then the pair carried the body up the pitcher walls, an equally tough job because the surface is slippery, thanks to a flaky wax that helps the pitchers entrap their prey. Slowly, the ants dragged the cricket to the underside of the pitcher rim, where a dozen other workers gathered to eat it.
What looks like theft turns out to serve the plant. By working in twos or threes, the little divers retrieve insect corpses several times their weight. These bulk items can’t be tidily digested by the plant and so tend to putrefy. Liquid fouled with ammonia and sullied by organic matter gives the pitcher plant the equivalent of acid indigestion and causes the pitcher to rot. The ants therefore aid the plant by removing large prey, but they also feed it: as my ant workers ate their cricket at the plant’s rim, small chunks of the insect dropped back into the liquid below, to be absorbed by the pitcher plant. For Camponotus schmitzi the pitcher is a first-rate “ant plant,” providing for its residents’ every need: housing and meat, and even sweets, in the form of the nectar at the rim of the pitcher that also attracts its hapless prey.
DOES SIZE MATTER?
Whether walking, swimming, climbing, or falling, an ant’s diminutive size influences how she travels through her world. Although we think of all ants as small, they vary in size several thousandfold. The average species has workers a little less than 3 millimeters (an eighth of an inch) long—smaller than a weaver ant and about the size of a marauder ant minor worker. But ants at the small end of the spectrum, such as Carebara atoma, the “atom ant,” are truly Lilliputian. I once dislodged a flake of bark from a tree in Singapore, only to expose four hundred yellow specks: an entire colony of its close cousin Carebara overbecki. The minor workers were almost the size of an atoma, their oval heads about as small as a single-celled paramecium. The slightly larger soldiers have elongated heads with two little horns.33
The ant worker at the other end of the scale, the major of the carpenter ant Camponotus gigas, is nowhere near the car size of the ants that terrorized Los Angeles in the 1950s cult film Them! At a little more than an inch long, she is indeed only fair-to-middling in size among insects and falls far below the world record holder for an adult insect, a female giant weta cricket I collected on Little Barrier Island in New Zealand (it weighed 71 grams, three times as much as a lab mouse). One scientist observed that ant species with bigger workers tend to show a greater number of behaviors, and he proposed this might be because of their larger