The parasitic fungi in the Cordyceps genus are a favorite subject of nature documentaries. They’ve also infiltrated popular culture via the zombie-apocalypse video game The Last of Us (2013) and its TV adaptation, in which a parasitic fungus mutates to infect humans. Scientists are keen to study Cordyceps to learn more about the origins and intricate mechanisms underlying these pathogen-based diseases.
The latest finding: DNA analysis revealed the same fungus in both parasitized insects and surrounding mosses, according to a paper published in the journal IMA Fungus. (Yes, really.) This suggests a second life stage during which the fungus lives inside the moss, possibly an evolutionary adaptation to survive when insect hosts may be scarce. It could also explain why the host species seems to prefer biting into mosses during their final death throes.
As we’ve previously reported, there are more than 400 different species of Cordyceps fungi, each targeting a particular insect species, like ants, dragonflies, cockroaches, aphids, or beetles. The spores attach to the target insect, such as a carpenter ant, and germinate, spreading through the host’s body via long tendrils called mycelia. Cordyceps essentially turns its host into a zombie slave, compelling the ant to climb to the top of the nearest plant and clamp its tiny jaws in a death grip around a leaf or twig.
The fungus then slowly devours the ant, sprouting through its head in one final indignity. The bulbous growths on the ends of the mycelia burst, releasing even more spores into the air to infect even more unsuspecting ants. It’s not a great way to go: The entire process can take four to 14 days. Prior research showed that the zombification might be due to the release of a special chemical that causes the muscles in the infected ants’ mandibles to contract forcefully for that death-grip bite.
A 2017 study found that the fungal cells formed an elaborate, interconnected 3D network, enabling them to communicate and exchange nutrients. They essentially cut the brain off from the rest of the ant’s body so the networked cells can control its behavior. And in 2019, scientists found that the fungus doesn’t actually directly attach to an infected ant’s brain. Rather, it breaks apart the membrane that covers jaw-muscle fibers, causing contractions strong enough to damage or destroy the muscle filaments that slide past each other when the muscles contract.