When we imagine an ant colony, we envision each ant doing their job, gathering food and resources to further grow their community. As the matriarch of the colony, ant queens are responsible for more than just giving birth to the entire colony – they must also save their brood from complete destruction before it occurs. If an ant larva is infected with a colony-threatening, virulent pathogen, the queen will eat the infected young before the infection develops, engaging in a form of “hygienic cannibalism.” This gruesome tactic of filial cannibalism is seen in termites yet remains relatively unexplored as a defense mechanism against infection for entire broods.
Most ant colonies fail due to predation, lack of food, or disease, and as the sole founders of the colony, the black garden ant (Lasius niger) queens are able to detect a change in the infected larvae’s cuticular hydrocarbons before the infection is able to be spread throughout the colony. The health of the queen remains unaffected as she sprays the larvae with her own acidic antimicrobial venom which neutralizes the pathogen when digested, leaving no trace of the infection.
A study conducted by Flynn Bizzell and Christopher D. Pull at the University of Oxford explores how the queen neutralizes the threat and the implications if the queen does not engage in filial cannibalism behavior. The began by exposing five larvae per tested queen to the fungal pathogen Metarhizium, which has the potential to wipe out the entire colony if left unchecked. The infected larvae were left in isolation for 24 hours for the infection to develop to a point where it was not transmissible, yet still lethal. A set of control uninfected larvae were introduced back to the colony along with the infected larvae to observe the rate of cannibalism. The queen cannibalized a whopping 92% of the infected larvae, and only 6% of the control group. Here, the researchers saw the queen accurately detect the infected larvae, activating the gland secreting the antimicrobial venom, and eating the entire carcass of the infected larvae, preventing the infection from developing and spreading to the colony. In a second round of testing, the researchers presented the queen with larvae whose infection had developed to the point where it had consumed the entire larvae carcass and was now highly virulent. The queens still utilized their antimicrobial venom, yet 80% of the queens contracted the disease and died, failing the colony.
Because queens live inside a sealed-in claustral cell, they aren’t able to simply take the infected larvae outside the colony like a worker would. The enclosed claustral cell also means that the queen must utilize all resources and nutrients with maximum efficiency. So by eating the carcasses of the infected larvae, these queens are recycling the nutrients of the larvae to be used to increase future egg production. This is very beneficial to founding queens who are not able to forage outside of their cell and thus have limited resources. The study reported that queens who cannibalized infected larvae laid an additional 55% more eggs than queens in a control group who did not eat their young. The larger the colony, the more successful it is in the face of neighboring broods competing for the same food and resources – therefore, the more infected larvae the queen eats, the more healthy larvae the queen produces.
Works Cited
Flynn Bizzell, Christopher D. Pull, Ant queens cannibalize infected brood to contain disease spread and recycle nutrients, Current Biology, Volume 34, Issue 18, 2024, Pages R848-R849, ISSN 0960-9822, https://doi.org/10.1016/j.cub.2024.07.062.
