Photograph by ANTCENTER, POLAND
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A Lasius niger queen ant dwarfs two worker ants.
Photograph by ANTCENTER, POLAND

Ant Queens Boost Their Immune System With Sex

Giving new meaning to Long Live the Queen: Scientists found that mated queens have stronger immune responses than their virgin sisters.

This story appears in the June 2018 issue of National Geographic magazine.

It’s good to be the queen—the ant queen, that is—because mating does wonders for her immune system.

When exposure to a low dose of a bacterium or virus builds an organism’s resistance to a later high dose of the same pathogen, it’s called immune priming. To study immune priming in invertebrates, Swiss and Panamanian researchers chose two that have plenty of time to build immunity: Lasius niger (above) and Formica selysi ant queens, which may live more than 20 years. Each species’ queens were sorted into two groups: the young virgin “princesses” and the mated queens—females that have mated with a male drone and stashed the proceeds in a “sperm pocket” from which they’ll fertilize tens of millions of eggs in a lifetime.

The researchers cultured a fungus that, in the wild, kills insects in about a week. They first administered a weak, low dose to each group of queens and then a high dose a week later. A tally of survivors showed that only one group, the L. niger mated queens, had gained immunity from the priming process. However, in both species, mated queens survived exposure to the fungus significantly better than did their virgin sisters.

The findings suggest that a queen’s dalliance with a drone “triggers an up-regulation of the immune system,” the study says. “The impact of mating on immune resistance was large and consistent.” In other words: With a boost from coital contact, Long Live the Queen.