It turns out that it takes a fungus to control one.
For the first time, researchers have discovered how an ant colony can survive an onslaught of zombie-fungus, also known as Ophiocordyceps, a behavior altering, deadly parasite.
Ophiocordyceps enters an ant's brain, causing it to march to its death at a mass grave. Once the ant is dead, the fungus produces more infectious spores.
In their new study, David Hughes, an entomologist at Penn State and his team describe a hyperparasitic fungus – that is, a parasitic fungus that exploits another parasitic fungus – that helps ants to ward off a zombie epidemic.
"In a case where biology is stranger than fiction, the parasite of the zombie-ant fungus is itself a fungus," Hughes said in a statement.
Ants are the dominant creature of all land-based ecosystems. In tropical forests, for example, almost 70% of individual insects are ants. They provide ample opportunities for scientific investigation.
Previous research has shown that ants groom each other and themselves to defend their colonies against pathogens such as fungi.
Hughes and his group modeled ant behavior in order to see grooming's effect on restricting infection. They found that combined with the ant's own grooming practices, the hyperparasitic fungus significantly limited the spread of the deadly, zombifying Ophiocordyceps.
Many ants become infected with the Ophiocordyceps fungus because it grows slowly, producing immature spores for about a month after killing its host.
However, the likelihood of an individual ant becoming a zombie is relatively low because the young spores are susceptible to the hyperparasitic fungus.
"Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading spores, fewer of the ants will become zombies," explained Hughes.