Ant queens practice a grim but effective form of childcare, eating their own sick larvae to recycle them into new, healthier eggs. A new study shows that by consuming their infected offspring, the queens protect the rest of their colonies from deadly infections while boosting their egg production with the influx of nutrients.
Researchers behind the study infected larvae with a type of insect-killing fungus from the genus Metarhizium. The fungus isn’t immediately contagious, so the ant queens had a small window to detect the threat, and most of them did. Queens in the study cannibalized 92% of larvae infected with the fungus, researchers found, while sparing most of the healthy larvae. Only 6% of the healthy young were eaten.
“Ant queens are remarkably effective at responding to and eliminating early-stage infections before they become transmissible,” the authors wrote, adding that this behavior, observed in the black garden ants (Lasius niger), one of the world’s most common, helps protect both the queen and the wider colony from collapse.
In cases where the infection was left to spread, 80% of the queens died. By not eating their infected larvae in time, they allowed the fungus to reach a lethal stage, eventually leading to the colony’s collapse. Queens that ate their sick larvae early stayed healthy.
The tough love of the surviving queens doesn’t stop at cannibalism. Researchers also observed queen ants spraying the infected larvae with acidic venom before feasting, which may help kill pathogens and explain how ant queens are able to safely consume infected larvae.
“Even though eating your own offspring may seem reprehensible to us, for many other animals, it is no more than an evolved and efficient way for parents to produce the most offspring they can over their lifetimes or to give the best care they can to a smaller selection of their offspring,” Aneesh Bose, a behavioral ecologist at the Swedish University of Agricultural Sciences, who was not involved in the study, told Mongabay in an email.
Queens that cannibalized infected larvae laid 55% more eggs than those that didn’t, leading the researchers to believe that they reinvest those nutrients into future reproduction. Ants live in confined spaces where disposal of dead bodies isn’t always possible, which adds another motivation for cannibalism.
“Filial cannibalism is a fascinating behavior because it goes against our basic nature and instincts, but it is hugely widespread elsewhere in the animal kingdom, and insects are no exception,” Bose added.
Banner image: Cannibalizing their offspring is often a life-or-death decision for the common black garden ant queen. Image by Lennart Tange via Flickr (CC BY 2.0).