Worker or Queen? A Supergene Gives Fire Ant Larvae a Head Start

Whether a fire ant larva grows up to become a small worker, a big worker or a queen depends largely on what the workers feed it. But a new study shows that its genes give it a head start too. Researchers at the University of Georgia found that a large block of genes in the red imported fire ant, Solenopsis invicta, pushes larvae towards a bigger body and a higher chance of becoming a queen. The study was published in Proceedings of the Royal Society B.

Fire ant workers come in very different sizes.

A supergene with two versions

Red imported fire ants come in two social forms: colonies with a single queen and colonies with many queens. Which form a colony takes is controlled by a supergene, a block of more than 500 genes that is inherited as one unit. It comes in two versions, called B and b. The b version arose about a million years ago and is linked to colonies with several queens.

Bigger with b

Haolin Zeng and Brendan Hunt set up queenless lab colonies of about 2,500 workers, using ants collected in Georgia in 2024. Some colonies got food with methoprene, an artificial version of juvenile hormone, the hormone that steers development. Two to three weeks later they weighed and genotyped more than a thousand worker pupae and nearly two hundred queen pupae.

• The hormone made a big difference: worker pupae in treated colonies were about three times heavier.

• The b version became more common as the ants got bigger: about half of the smallest workers carried it, about 65 percent of the largest workers, and 75 to 83 percent of the queens.

• On average, pupae with two B copies weighed about 19 percent less than pupae with one B and one b.

When the researchers compared which genes were active, they found 34 genes that were also more active in pharaoh ant larvae on their way to becoming queens. One of them, a gene called gas8, showed up in every comparison and sits inside the supergene. What exactly it does in fire ant development has not been tested yet.

What it means

Feeding and hormones still decide most of the outcome, but genes can tilt the odds. For fire ants, that may help explain how multi-queen colonies keep producing so many new queens, one of the reasons they spread so successfully as an invasive species. Fire ants are not a good species to keep, by the way: read why Solenopsis is not a good idea. Want to know how dangerous their stings are? Read can an ant sting kill you?. US readers can also check our guides on why not to keep fire ants and invasive ant species in the United States.

Sources

• Zeng, H. and Hunt, B., 2026. Proceedings of the Royal Society B.

• Earth.com, 2026. Worker or queen? A genetic advantage may shape a fire ant's future.

Photo: © Emmett Collins-Sussman