Sunday, February 3, 2002		Nature

Winged scavengers of another kind
Nutan Shukla

BESIDES vultures, another winged scavenger is a type of tropical stingless bee. It is known to supplement its diet of pollen and nectar with meat. To tackle a carcass, some workers form a circle and tear at the skin to make a small hole. Then other workers go in and work from inside. As they chew, they spread an enzyme over the meat. This partially digests the food so that it can be carried back to the nest, where it is regurgitated to others.

About a few years back on Thanksgiving Day, an American scientist was working in Panama and he put out the carcass of the traditional Thanksgiving turkey for the local cats to enjoy. It was a great surprise for him when he noticed that the first of the scavengers to converge on the carcass was a swarm of bees. On taking a close look, he found that these insects were stingless bees that had previously been seen over dead bodies, but it was thought they were only after the body juices. When the scientist examined them more closely, however, he found that they have five large, pointed teeth on each mandible, a rather unusual arrangement for bees to have, and he discovered that they use these to cut through flesh.

The modus operandi of these insects is to scout the bees’ head out from the colony and search, not for flowers, but for carrion. Usually dead frogs, lizards and such type of animals are preferred. During the course of their search if they find a suitable carrion, they lay down their specific pheromone (smell) trail and recruit more help. The bees then descend in large numbers on the body. If there is any competitor, such as flies, is frightened away and the bees take over.

First, they settle on the outside of the carcass and form a circle. Using the specially adapted mendibles, they begin to tear at the skin, making a hole through which the rest of the swarm can enter and eat away the insides. A frog is reduced to its bare bones by 60-80 bees in about 3 hours, but a thousand strong swarm may tackle a dead monkey or ant-eater and strip it down in a few days.

Aiding and abetting them might be a species of ants. The ants appear to be tolerated by bees, some kind of chemical interaction between the ants and the bees preventing the latter from ousting the former from the site. The mutual tolerance is aided by the fact that the two species work a shift system: bees by day and ants by night.

However, bees are one of the most dreaded creatures of the insect world, but still they are fooled by other insects. Most insect brood parasites behave in much the same way as cuckoos, and lay their eggs in other insect’s nest. For example, bomber-flies are one such group of insect cuckoos. They leave their eggs with ground-nesting bees, but avoid any conflict with the host by laying their eggs without entering the nest. The bees’ nests have vertical entrance tunnels, and the bomber-fly hovers over an entrance and bombards it with eggs.

The accuracy of the fly’s aim is astonishing. Its eggs bounce down the tunnel and come to rest close to the mass of pollen that the bee has painstakingly collected to feed its own larvae. The bee larvae eat the pollen, and then, in turn, the bomber-fly youngsters feed on the fattened bee larvae.