Scientists have found that sick young ants release a smell to tell worker ants to destroy them. They do this to protect the rest of the colony from infection. But they noted that queens did not seem to commit this act of self-sacrifice.
Many animals hide their illness for social reasons. For example, sick humans often risk infecting others so they can still hang out with friends or go to work.
But ant colonies act as one “superorganism”. This means that the ants work together to ensure the survival of all. According to an Austria-led team of scientists, an ant colony’s response to sickness is similar to how infected cells in humans send out a “find-me and eat-me” signal.
Disease in the colony
The lead author of the new study is Erika Dawson, a behavioural ecologist at the Institute of Science and Technology Austria. Ant nests are a “perfect place for a disease outbreak to occur because there are thousands of ants crawling over each other”, Dawson said.
When adult worker ants get an illness that could spread through the colony, they leave the nest to die alone. But young ants, known as pupae, are trapped in a cocoon, making it impossible for them to isolate themselves.
Scientists already knew that when these pupae have a deadly illness, there is a chemical change that makes a certain smell. The scent tells worker ants to destroy both the pupae and the disease that threatens to hurt the colony (see graphic).
For the new research, the scientists wanted to figure out if the pupae were actively telling other ants to kill them, Dawson said.
A willing sacrifice
First, the scientists extracted the smell from the sick pupae of a small black garden ant called Lasius neglectus. When they applied the smell to healthy pupae in the lab, the workers still destroyed them.
Then, the team conducted an experiment showing that the sick pupae only made the smell when worker ants were nearby. This proved it was a purposeful signal for destruction.
“While it is a sacrifice ... it’s also in their own interest because it means that their genes are going to survive and be passed on to the next generation,” Dawson said.
However, there is one member of the nest that does not sacrifice itself.
The team found that when queen pupae are infected inside their cocoons, they do not send out the smelly warning signal.
“Queen pupae have much better immune systems than the worker pupae, and so they were able to fight off the infection – and that’s why we think that they weren’t signalling,” Dawson said.
Dawson hopes future research will investigate whether queen pupae sacrifice themselves when it becomes clear they will not beat their infection.
The study was published in the journal Nature Communications.
