Invading fungus controls zombie ants, study says

Researchers have made the surprising discovery that the so-called zombie ant fungus invades the ant's entire body without infecting its brain.

Ed Mason | Oct 29, 2019

A new study led by Penn State researchers is shedding light on the way zombie ants fall victim to a deadly invading fungus that controls their movements and eventually kills them.

The study is published in the Proceedings of the National Academy of Sciences.

Earlier research demonstrated that the zombie ant fungus elegantly named Ophiocordyceps unilateralis sensu lato controls the behavior of carpenter ant workers, forcing them to climb vegetation and attach to the underside of leaves or twigs, where they expire. The fungus grows inside the cadaver until it grows a stalk that protrudes from the ant's head and then discharges deadly spores onto living ants foraging on the ground below.

Scientists previously believed the fungus exerted control over an ant by invading its brain. But the Penn State study is overturning that assumption.

Using 3-D computer modeling and artificial intelligence to analyze samples, the researchers made the astonishing discovery that the fungus invades the ant's entire body without infecting the brain.

The fungal cells infect muscle fibers and may form a 3-D network that allows the parasite to control the ants like a puppet master, the researchers say.

"Normally in animals, behavior is controlled by the brain sending signals to the muscles, but our results suggest that the parasite is controlling host behavior peripherally," said senior author David Hughes, an associate professor of entomology and biology at Penn State, in a statement. "Almost like a puppeteer pulls the strings to make a marionette move, the fungus controls the ant's muscles to manipulate the host's legs and mandibles."

It is possible the fungus chemically alters the ant's brain without actually invading it.

"We hypothesize that the fungus may be preserving the brain so the host can survive until it performs its final biting behavior that critical moment for fungal reproduction," said Hughes. "But we need to conduct additional research to determine the brain's role and how much control the fungus exercises over it."