We humans have Tinder, Hinge, eHarmony and Grindr. For other animals, there's a real dearth of matchmaking services, not even Bumble or Plenty of Fish.
But for future queens of one ant species, sterile worker ants seem to serve this function by physically carrying their royal sisters to neighboring nests. There, the queens-to-be can mate with unrelated male ants, according to a new study published in Communications Biology.
"This is quite exciting," said Jürgen Heinze, a zoologist at the University of Regensburg in Germany and a co-author of the study. "It's the first case of this assisted mate choice and assisted outbreeding that we have in animals."
If you looked at the ground by riverbanks on the Mediterranean, you might occasionally catch a glint of sunlight reflecting off the wing of a Cardiocondyla elegans queen ant. But the queen would most likely not be flying, or even walking. Instead, she would be riding piggyback atop a worker ant, gripped firmly by a worker's mandibles.
Once you look for the carrying behavior, "you only see these little ants moving around," said Mathilde Vidal, a doctoral candidate at Regensburg and lead author of the study.
From 2014 to 2019, the researchers mapped the location of 175 Cardiocondyla ant colonies in southern France and recorded 453 instances of this carrying behavior.
Though these workers are tiny — only 2-3 millimeters in length — they have been observed carrying the queens almost 50 feet from home before dropping off their sisters at the entrance of a foreign nest. And the workers seemed to know where to go, traveling in more or less a straight line and skipping nests that were closer.
As it is for all sexually reproducing organisms, choosing the right mating partner is an important decision for Cardiocondyla elegans. But this species faces a particular problem: The male ants have lost their wings and remain trapped in "mating chambers" near the nest entrance where they regularly mate with related females.
Excessive inbreeding can be detrimental. In a 2006 study, Heinze and his colleagues found that prolonged inbreeding in another species of Cardiocondyla had led to unhealthier ant colonies.