Cooperative insects like bees and wasps all pitch in for the good of the hive, raising the queen’s offspring without a thought toward producing their own, right? Not so fast—in the common wasp, about one percent of workers defect from their own hives to lay eggs in a foreign one.
That’s a pretty risky proposition unless that colony’s queen has died. Surprisingly, the defectors snuck into colonies with and without queens at equal rates. But drifters to queenless colonies were about twice as likely to have become fertile as drifters to colonies with queens.
This type of intra-species parasitism happens in other insects, including paper wasps and some bees. But this is the first evidence for it in the common wasp, a species found in Europe, North America, Asia, Australia and New Zealand.
“We believe that this is a very common phenomenon in social insects,” says Ricardo Oliveira at the University of Leuven in Belgium.
Among social wasps, workers are females that never mate. They can only lay unfertilized eggs, which hatch into male drones. Their one chance at having grandchildren is for these males to reach adulthood, fly away and mate with a queen in another hive.
Normally, the native workers in a hive of wasps are as much as 99-percent effective at sniffing out and eating any eggs that don’t belong to the queen, a behavior called policing. But it’s not uncommon for queens to die, particularly toward the end of the season in late summer or early fall.
“If the queen dies, then it can become a free-for-all,” says David Nash, a biologist at the University of Copenhagen who was not on the study team. Workers and drifters alike lay eggs in a last-ditch attempt to pass on their genes to the next generation.
To test whether wasps would be more likely to drift to colonies with or without queens, Oliveira and his colleagues collected four wasp colonies and removed the queens from two of them. The team then dabbed a bit of paint on each worker wasp, using a different color for each colony. At the end of two weeks, they killed all the workers and recorded which colony they originally came from based on their paint markings.
Oliveira then dissected the workers to see if their ovaries were ready to lay eggs. When dissecting a worker wasp, you can tell right away if it's fertile, he says. Undeveloped ovaries are so tiny that they’re hard to find. “If they’re developed, it’s the first thing you see,” he says.
The scientists performed this same experiment four times from August 2013 to July 2014. They found that workers were more likely to drift from colonies with a queen than those with no queen. Surprisingly, though, the workers drifted equally to colonies with and without queens, they report in a paper published in January in Animal Behaviour.
When Oliveira measured each colony’s volatile chemicals—odors and other chemicals that waft on the air—he found no differences between colonies with and without queens. It’s possible, then, that drifters simply can’t tell whether the nest they are invading has a queen until they get inside.
“Once they enter the colony, they have cues on the workers themselves and the paper combs,” says Nash. “These non-volatile cues they detect by rubbing their antennae” to pick up the queen-revealing chemicals.
Crucially, drifters to queenless colonies were more likely to try to lay eggs. In hives with a queen, 2 percent of native workers and 12 percent of drifters had developed ovaries. In hives with no queen, 20 percent of both drifters and native workers had active ovaries.
It's still not clear whether the drifters in either scenario are successfully laying eggs that go on to become adult wasps. Since 2013, Oliveira has been collecting common wasps in Belgium and freezing them in his lab, ready to extract their DNA, so he plans to do further genetic testing.
Even if drifters are managing to produce offspring, it's also not yet known what sort of advantage the wasps get from this sneaky behavior.
It could be because, if you want to maximize your chances of passing on your genes, stealing resources from an unrelated hive for your offspring is better than stealing resources from your sisters, who share much of your genetic material. But Nash says it could be completely the opposite.
Even though drifters selfishly lay eggs in the new colony, they presumably don’t sit idle the rest of the time, and the work they do caring for young and for the hive might provide a net benefit to the colony. In that sense, drifters could be diligent workers helping out their new homes, perhaps because they’re related to the colony.
“It’s possible that you’re quite closely related to the nearby nests,” he says, “if the nest was founded by the sister of your queen.”