Ants get cues to remove their dead: Study

How do ants know whether their friends are still alive?

It is the chemical compounds which signal that an ant is still alive and prevent its comrades from taking it to the colony graveyard, suggests a new study which provide details of the process used by insects to the dead nest mates.

Necrophoresis, the removal of dead colony members from the nest, is an innate hygienic behaviour exhibited by ant species that live in large colonies in enclosed nests.

Previous studies about the process suggest that ants get cues to remove their dead co-workers from their nest because of the formation of decomposition products in the corpse.

Contrary to these findings, study published in the US journal 'Proceedings of the National Academy of Sciences', says that disposal squads of ant colony swing into action within one hour of the death of any member, much before the buildup of decomposition products starts in a corpse.

Dong-Hwan Choe and co-researchers from University of California found that chemical cues for removal of body are always released by an ant but other chemicals compounds, which are  present only in live ones, suppress them.

Once an ant dies the chemicals found in alive worker dissipate making the cues for removal of the deads overt, said Choe.

Using the basic nature of worker ants, scientists tried an innovative method to understand Necrophoresis. The workers normally retrieve pupae and return them to the nest.
     
Scientists tried to see if they do the same with pupae which are laced with chemicals released by dead ants.

The study team rubbed the pupae with the extracts from the cuticles of the freshly killed ants and those which were left dead for an hour.

"When pupae were rubbed with the extracts and left outside, only those treated with extracts from freshly killed ants were ignored without being carried," Choe said.

The analysis of these compounds revealed presence of two chemical dolichodial and iridomyrmecin, which a live worker secretes on its cuticle.

"But within 40 minutes, if not continuously refreshed, dolichodial and iridomyrmecin either evaporate or become inactive thus leaving only those compounds which act as cues for removal of corpse," the authors found.