Heroic sick ants die alone to save colony
Infected with a contagious parasite, ants martyr themselves by voluntarily leaving the nest to save their kin.
Tue, Feb 16, 2010 at 01:01 PM
Photo: Todd Palmer/Science/AP
Ants are social creatures, sticking with their colonies through thick and thin — except when they’re ill with an infectious disease, in which case they’ll leave the nest and bravely face death alone in order to save their nest mates.
The BBC reports that scientists made this astonishing discovery while observing ants of the species Temnothorax unifasciatus. When individuals within the colony became infected with a deadly parasitic fungus, they voluntarily walked far away from the nest days or hours before death.
"Our study suggests that infected ants at least in some species walk away from a colony and die alone, rather than risk infecting others," Professor Jurgen Heinze told the BBC.
Though many types of parasitic fungi are able to turn their victims into zombies — orchestrating their movements according to the parasite’s best interests — that was not the case with T. unifasciatus ants and the Metarhizium anisopliae fungus.
The researchers exposed a small sample of both infected and uninfected ants to CO2 to artificially reduce their life spans, and found that even the uninfected ants left the nest, knowing that death was forthcoming.
"This simple experiment demonstrates that nest leaving is not caused by parasite manipulation but by the imminence of death," biologist Michel Chapuisat confirmed to the BBC.
That the ants did so of their own volition rather than being carried out by other workers is significant, Chapuisat notes.
Interestingly, this behavior is the direct opposite of that of another social insect, the bumblebee. Bees infected with fly larvae leave the nest not to protect their nest mates, but in an attempt to save their own lives. Exposure to cold air slows down the life cycle of the parasite.