The modus operandi of the Cordyceps fungi is the stuff of nightmares. These parasites grow inside their insect hosts by feeding off the non-vital organs, and manipulate the hosts’ behaviour so that they can reproduce. When it is ready to produce spores, the fungus grows into the brain and releases chemicals that make the host climb a plant then attach itself near the top. It then kills its host by devouring its brain, before sprouting a mushroom from the top of its head, which disperses its spores as widely as possible.
Cordyceps fungi can decimate entire ant colonies, but some colonies can keep an infestation at bay and survive for long periods of time. A new study now reveals how they do so. It turns out that the zombie-ant fungus is itself parasitized by another fungus, which limits its ability to reproduce and prevents it from overwhelming the colony. This microbial defence system allows the two species to stably co-exist and ensures the long-term survival of the colony despite a high rate of infection.
Cordyceps manipulate worker ants to leave their nest and march off to a nearby site where they will eventually meet their fate. These sites are mass graves littered with the bodies of nest-mates that have succumbed to the fungus. They can persist in the same location for years, growing steadily as ants arrive one by one to die.