New ant species plunders other ants’ farms

Some newly discovered ants aren’t exactly vandals sacking Rome, but they pillage valuable real estate nonetheless.

A raider ant (topmost) grapples with a burly farmer for rights to the gray fungus. Adams

The new species, in the genus Megalomyrmex, specializes in raiding the nest gardens of fungus-cultivating ants, say Rachelle M.M. Adams and Ulrich G. Mueller of the University of Texas, Austin and their coauthors.

The raiders chase away the original farmers but don’t fertilize the farm. The usurpers eat the dwindling fungus and chop up the farmers’ left-behind larvae as baby food for their own young. The bounty eventually runs out and the raiders move on, say the researchers in the December 2000 Naturwissenschaften.

Megalomyrmex and other ants are known for their thieving ways. While some ant species raid farms to eat larvae, others infiltrate fungus gardens as phony nest mates that don’t help with farm chores. The new species might represent a missing link between these two lifestyles, Mueller speculates. Until now, he says, “no one has documented raiding for the sake of the gardens.”

Four colonies of the raider species, not yet officially named, turned up in Panama as the scientists were collecting walnut-size masses of fungus farms tended by two species of Cyphomyrmex ants.

Back in the lab, the researchers offered the raiders a series of ant farms tended by cultivating species. Typically, a raider scout discovers a farm, and an attack party rushes in with aggressive postures.

To human eyes, the raiders look slightly undersized. Although each of the species matures to lengths of 2 to 3 millimeters, the farmers grow “bulkier,” as Adams puts it. Still, the farmers don’t fight. “They run away or curl up and hope nobody notices them,” she says. As they flee, some rescue larvae or a bit of fungus.

The raiders prove adept at fungal nesting, tearing off bits of the sticky mass to create a cavity for their larvae and queen. They also patch divots and plug all but one tunnel using their forelegs to pat wads of fungus into place with the facility of a lifelong inhabitant.

The raiders seem to prevent weed outbreaks, too. They can feed on a fungal farm for weeks, but if researchers remove them, rogue molds overrun the nest in a few days.

Despite such skills, the raiders “don’t know how to manure the garden,” Mueller says. They ignore caterpillar droppings and other treasures that farmer ants use to nourish the fungus.

Alfred Buschinger at the Technical University of Darmstadt in Germany welcomes the work as “sound.” Little is known about Megalomyrmex behavior, he says. He hopes the researchers will find more colonies to double-check their findings.

The discovery of such raiders fits into Mueller’s work on the variety of crops raised by farmer ants (SN: 11/21/98, p. 334). Diseases can drive a farmer to a desperate experiment with a new cultivar, but so can raids. Mueller says, “If you’re a farmer and you’re attacked by Vikings, what can you do?”

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.