Study reveals why ant queens eat infected offspring

Ant queens eat their infected offspring at the first sign of illness and then recycle them into producing new eggs, a new study has revealed.

The study, carried out by researchers at Oxford University’s Department of Biology, is published on the institution’s official X handle.

The study reveals that ant queens typically found new colonies on their own and, at the early stages, are highly vulnerable to their brood being wiped out by disease. The scientists discovered that killing off sick larvae before they became infectious could be a strategy used by queens to combat this threat.

Test

To test their discovery, researchers presented founding queens of the black garden ant with larvae infected with a fungal pathogen, Metarhizium, for 24 hours.

“At this point, the infection was lethal (sufficient to cause death), but not yet transmissible,” the study said.

According to the study, the queens ate 92 per cent of the infected larvae, leaving no remains—but only 6 per cent of the control larvae that had not been infected.

A control is an element that remains unaffected by other variables in an experiment. A control is used as a benchmark, serving as a point of comparison against which other test results are measured.

“Once the queens find a sick larva in the brood pile, they get to work immediately and spend several hours chewing them up until they’re all consumed,” Chris Pull, lead researcher, said.

According to the study, despite the potential risk of getting an infection, all the queens survived after eating the infected larvae.

The scientists suggest that the queens may protect themselves by swallowing an acidic, antimicrobial venom produced by a special gland at the end of their abdomen.

“Indeed, some of the queens were seen massaging the opening of this gland during and after cannibalism.”

The queens that ate their infected larvae went on to lay 55 per cent more eggs than non-cannibalised control queens, indicating that the nutrients from the ingested offspring were recycled for production.

“Ant queens start their colonies alone and essentially starve themselves to raise their first workers. The queens who produce the most workers have the best chances of survival, so being able to eat and recycle infected larvae back into brood production means valuable resources are not wasted,” said co-author, Flynn Bizzell.

The queens, however, declined to eat infected larvae, which had progressed to the infectious (transmissible) stage. They rather sprayed the infectious with their anti-microbial venom as though to attempt to control the infection.

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“Even so, most (80%) of the queens still contracted the disease and subsequently died. Acting early, before larvae become infectious, is key,” the study advised.

The researchers said that “hygienic cannibalism” is only observed in queens and not among mature worker ants. This may be because, unlike queens, which seal themselves into nests, worker ants can dispose of infected larvae by carrying them out of the nest.

“Our results provide compelling evidence that cannibalism solves the problem of disease containment and corpse disposal in the confined space of founding queens underground bunker, whilst also ensuring valuable nutrients are not wasted – and that this improves their chances of successful colony foundation,” said Mr Pull.