Ants raise other insects as food, like we do with cows
Species: Melissotarsus insularis and three other Melissotarsus species
Habitat: Down on the farm under the bark of African trees, particularly in Madagascar.
Lots of ants practice a rudimentary form of agriculture. Some are gardeners, gathering leaf fragments on which they cultivate a crop of tasty fungus. Others are dairymaids, “milking” the sweet excretion known as honeydew from aphids, scale insects and other related insects.
But the Melissotarsus ants of continental Africa and Madagascar are special. If biologists’ best guess proves correct, these ants raise their insect herds for meat, not milk – the first example of meat farmers other than humans. And that’s not all. The insects they cultivate may be the best example of true domestication outside of our crop plants.
You have to know what you’re looking for to even see Melissotarsus. The ants – barely 3 millimeters long – live most of their lives within the intricate gallery systems they excavate in and under the bark of trees. They’re such committed burrowers that their second pair of legs points up, not down, so they can get a foothold in the tunnel roof as well as the floor. They share their galleries with several species of armored scale insects, so-called because most species secrete a tough, waxy scale that covers and protects them.
But the ants’ charges aren’t paying for their keep in the usual way, with honeydew. In fact, they apparently lack a complete gut and thus are incapable of making the stuff. Nor are the ants nibbling at the waxy scale – the scale insects tended by the ants, despite their name, have no scale, and some even lack the wax glands needed to produce it. “Armored scales just don’t seem to be equipped to produce an exudate that’s enough to satisfy an ant,” says Scott Schneider, an entomologist at the University of Massachusetts at Amherst.
Savor the flavor
So what do the ants get from all their work housing and protecting the scale insects? Almost the only remaining possibility is that the ants sometimes make a meal of the insects themselves, Schneider reported at a recent meeting of the Society for the Study of Evolution in Norman, Oklahoma. No one has yet caught Melissotarsus in mid-munch, partly because the ants like their privacy and quickly seal off any peepholes into their galleries. Next year, however, Schneider will measure stable isotopes in the ants’ bodies, which will indicate whether their diet is mostly plant or animal in origin.
If the ants are indeed eating the scale insects, they may have selected livestock that lack the hard, inedible scale because it makes them easy to eat. In paralleling what humans have done in breeding their crop plants – corn, for example, is much less armored than its ancestor, teosinte – the ants may have created the clearest case of domestication ever seen in non-human animals, says Schneider.