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Ants and the problem of impostor mothers

The views expressed are those of the author and are not necessarily those of Scientific American.


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In honor of Mother’s day, I present a portrait of a Tennessee winnow ant with her mom.

Aphaenogaster tennesseensis

But wait! This scene is not as heart-warming as it may seem. This mother has a dark past of murder, impersonation, and trickery.

To explain the story, I’ll start with a perhaps oversimplified observation about ant families. Ants are everywhere, of course. And one reason for the global domination of ants may be how the little insects handle motherhood.

Ant mothers enlist their first, usually sterile, children- often by the tens of thousands- to raise the fertile ants that later to go into the world to start new colonies. Ants unconcerned with their own reproduction can be fantastically productive as adults, so a mature, thriving colony of neuter workers is a powerhouse. Insect societies churn out the seeds of new colonies at a rate inconceivable for a lone ant mother. Essentially, ants have figured out  they can make a great deal more ants by specializing into many industrious helpers and a few, often just one, mothers.

But growing a large, healthy colony from scratch is difficult. Young queens strike out on their own, alone, where they risk being eaten by spiders, birds, fungi, and even other ants. They have to find a suitable homestead. They have to dig the first nest chambers. They wait patiently for months, or even years, while the nascent colony struggles and expands. Most queens, more than 99%, fail before the colony reaches maturity.

It is a great deal easier, for a prospective ant mother, simply to take over an established nest. Such a hostile takeover is precisely the strategy of a surprising number of species. The Tennessee winnow ant, Aphaenogaster tennesseenis, is one of them.

An Aphaenogaster tennesseensis queen in a recently-invaded nest of its host, Aphaenogaster rudis (Manhattan, Kansas, USA).

She is a lithe, clever little insect. After mating, she searches out an existing colony of woodland winnow ants, kills the resident queen, and chemically dupes the workers into treating her as though she were their own mother, rather than a stealthy parasite usurping their fortress.

The parasitic queen is highly attractive to duped workers of the invaded colony.

Workers automatically turn to clean, feed, and tend to the impostor.

Once the colony is hers, the parasite queen lays eggs while the beheaded empire continues to build, gather food, and defend its territory. As her own worker offspring emerge and the older host workers die off, the colony transitions through a mixed composition of two species to a final composition of just the parasite. After this point, the colony functions much as any other ant colony.

Anyway. Happy Mother’s Day! And, if you’re an ant, just double-check to make sure your mom is the right species.

Alex Wild About the Author: Alex Wild is an Illinois-based entomologist who studies the evolutionary history of ants. In 2003 he founded a photography business as an aesthetic complement to his scientific work, and his natural history photographs appear in numerous museums, books, and media outlets. Follow on Twitter @myrmecos.

The views expressed are those of the author and are not necessarily those of Scientific American.





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