A deadly fungus sometimes infects the larvae of the black garden ant (Lasius niger).
If the fungus is allowed to develop to the point that it becomes contagious, it will not only kill the infected individual, but also all the other larvae in the colony. The queen – the mother of all the larvae – also has an 80% chance of being killed.
How do queen ants deal with this cataclysmic threat to their colony?
In a recent study, researchers found that queens cannibalise their infected young, chewing them up and swallowing them so that nothing remains.
The queens may first try tending to the sick larvae rather than killing them, but when an individual can no longer be saved from dying, the queen’s behaviour changes.
“It switches from them trying to care for that individual, to killing that individual for the benefit of the colony,” Dr. Christopher Pull tells BBC Wildlife. “As soon as that individual becomes a risk to the rest of the colony, it's eliminated to prevent further infections.”
Eating their infected young provides queens with the nutrients they need to produce more offspring. Essentially, the infected larvae are recycled into future siblings.
But why doesn’t the queen become infected with the fungi when she eats her infected young?
The ants have a special gland that produces an acidic, antimicrobial venom. This is usually used to clean up the nest, in the same way we might use bleach in our bathrooms, and to deter predators. The ants also use it on each other, “like a carefully applied chemical disinfectant,” Dr. Pull says.
The researchers noticed that the queens used their venom gland to spray infected larvae, and groomed the gland while eating their young, suggesting that the acidic and antimicrobial properties of the venom might be helping the queens to destroy the fungus.
How exactly the queens know which offspring are infected is not yet known, but the researchers think that queens might detect infected larvae through the larvae’s own signals.
“The larva is likely emitting a cue that elicits its own destruction,” Dr. Pull says.
So, the larva is likely to be telling its mother – through chemicals – to come and eat it.
This has probably evolved because only queens reproduce. In terms of passing on genes, this means it’s actually in the larva's best interest for its mother to survive, and so – brutal as it may seem – for it to become a meal for its mother.
Main image: Katja Schulz from Washington, D. C., USA, CC BY 2.0 <https://creativecommons.org/licenses/by/2.0>, via Wikimedia Commons
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