Queen Ants Eat Sick Young to Protect Their Colony

Queen ants and hygienic cannibalism

Ant mothers may be the ultimate practitioners of tough love: they have no opportunity to pamper sick offspring.

US researchers have discovered that when a newly hatched black garden ant larva encounters a pathogen, its queen will consume the entire grub-like body before it can become infectious.

Known as ‘hygienic cannibalism’, this behaviour prevents the queen and other larvae from becoming ill while they are enclosed together in the nest. It also gives the mother additional energy for producing eggs in the next breeding attempt.

"Ant queens start their colonies alone and essentially starve themselves to raise their first workers," explains biologist Flynn Bizzell from the University of Oxford.

"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."

Bizzell and fellow University of Oxford biologist Christopher Pull found that worker ants from established colonies do not display this same inclination towards cannibalism.

In certain ant species, workers and soldiers have even been observed giving medicine or performing life-saving operations on unwell or injured nestmates. Such interventions are not viable, however, in the nursery of a black garden ant (Lasius niger), particularly during a colony’s earliest stage.

Why black garden ant queens act quickly

At this precarious point, queens cannot simply remove diseased larvae from the nest. They are shut inside with their offspring in a crowded space, without any other ants available to assist them.

The danger of infection spreading under these conditions is too great for a queen to overlook. Once she identifies a pathogen in her nest, she eliminates every infected larva she can locate as rapidly as possible.

The researchers determined that, when necessary, a queen will cannibalise 92 percent of infected larvae. Queens that take this action are able to lay 55 percent more eggs during the following attempt.

For their recent experiments, Bizzell and Pull exposed five larvae belonging to each queen to infectious spores from a fungal pathogen.

The larvae were kept apart for 24 hours, allowing the fatal infection to develop, though they had not yet become contagious at that stage. After the infected larvae were put back into their nest, Bizzell and Pull observed the queens’ response.

Over the course of several hours, the mothers chewed their larvae. They ate nearly every sick individual, yet allowed most healthy larvae to survive.

Venom may protect queen ants from infection

The fungal pathogen apparently did not affect the queens, including those that had consumed it. Bizzell and Pull suspect the ants may protect themselves internally in some way.

Before and after queens were seen feeding on their offspring, the biologists noted that some ants groomed a gland on their abdomens. The gland creates an acidic venom with antimicrobial properties; if ants swallow this venom, it may neutralise the pathogen within their gut.

In additional tests, queens were given diseased larvae that had already died and started developing fruiting bodies containing infectious spores. The queens groomed the corpses and sprayed them with venom from this gland.

This later phase of infection is evidently highly dangerous for the queen, however. Even after spraying the larvae, she died from the infectious disease almost 80 percent of the time.

When a queen survived, her brood did not: secondary infections killed them all. Early action to stop the disease spreading is therefore important.

The results indicate that queen ants consume their young as a disease-adaptation strategy, safeguarding both their own survival and that of their present and future offspring.

There is nothing quite like a mother’s care.

The study was published in Current Biology.