Zombie ant fungus (Ophiocordyceps species) is an endoparasite (=growing inside their host) that infects certain species of ants. Now almost every insect hobbyist would have seen pictures of zombie ant fungus in social media.
The infection cycle of zombie ant fungus
What the endoparasite do is they infect ants when they are out looking for food. When the ants are infected, for 2 to 3 weeks, they go about their usual business, unaware that they are about to become ‘zombie ant’.
When the endoparasite is ready to continue the next stage of its life-cycle, i.e. infecting other ants, they will ‘tell’ the ants to leave the nest and bite into parts of leaves or stalk.
Then the fungus will grow out of the ants’ body to a stalk from which fungal spores are produced and released. The unfortunate healthy ants that pass by during the fungal spores releasing time will get infected and the cycle will continue.
Can other ants ‘recognize’ infected ants?
Since we are not ants, we don’t know whether infected ants carry any ‘symptoms’. And if they do carry any symptoms, can their nest-mates recognize and do something about it?
A group of researchers from Penn State University set to test the question of whether sick ants carry any symptoms and whether healthy ants can recognize infected ants, and if they do, what are their responses?
In ants’ world, symptoms would mean being anti-social. A healthy ant would engage in a social activity called trophollaxis (kissing to exchange liquid food) regularly. If the infected ants experience any symptoms, the researchers think they will do fewer trophollaxis and possibly spent more time alone, being away from the crowd.
If healthy ants can recognize infected ants, what they will do (in ants’ world) is to attack the infected ants, kill it and subsequently disposed of it far far away from the main nest.
Zombie fungus wears an invisibility cloak
After 1,240 hours of observations on the interactions of healthy and infected ants, the researchers could not see any sign of ‘infected’ ants being more anti-social, or healthy ants showing any aggression towards ‘infected’ individual.
In every aspect of the behaviour, infected ant behaves no different from any other healthy individual. In conclusion, even though the researchers have no idea HOW the zombie fungus cloak themselves from being detected, the bottom line is they do and they do it so damn well!
Source: Sola-Gracia E, de Bekker C, Hanks EM, Hughes DP (2018) Within the fortress: A specialized parasite is not discriminated against in a social insect society. PLoS ONE 13(2): e0193536.