I’ve covered some ants in the past, discussing their fungal friends that provide them food, as well as their foes that turn them into zombies. A recent article by a team of researchers that included members of the Smithsonian Tropical Research Institute has found that most species of leaf-cutter ants have a practice that helps defend their young against parasitic fungi: wrapping them in the same fungi that they use to digest the leaves they bring underground!

Sarah Puschmann reports:

In the dark recesses of an underground fungus garden, a Panamanian leaf-cutting ant plucks a tuft of mycelia, the wispy part of the basidiomycete fungus these ants grow and eat, and carries it to a nearby ant pupa. The ant licks the pupa’s body before patting the fungus into place, continuing until it appears, when viewed under a powerful microscope, as though the pupa is webbed in short strands of spaghetti.

Odd behavior perhaps, but leaf-cutting ants aren’t the only ants to cover their pupae in mycelia. In a 2012 study scientists showed that of 20 species of fungus-growing ant (including the leaf-cutting ant), the majority cover juveniles—eggs, larvae and pupae—in mycelia. The research, published in the journal Evolution, was authored by Hermógenes Fernández-Marín of the University of Copenhagen, the Institute of Scientific Research and High Technology Services and the Smithsonian Tropical Research Institute; William T. Wcislo, senior staff scientist at the Smithsonian Tropical Research Institute; and Sophie A. O. Armitage and Jacobus J. Boomsma of the University of Copenhagen.

“This [finding] was nice because the fungi is really the food for the ant, but in this context the ants co-opt the fungi for protection,” Fernández-Marín says.

In 2012, scientists  weren’t certain  what exactly the mycelial cover was protecting the ants against. Now, they may have an answer: The fungal cocoon impedes a parasitic fungus. In a new study in the Journal of Animal Ecology, Fernández-Marín, Wcislo, Armitage and Boomsma suggest that for the leaf-cutting ant Acromyrmex echinatior, this fungal cocoon slows down a known enemy: the parasitic fungus Metarhizium brunneum.

While an ant is out foraging, spores of this parasitic fungus can land on it, burrow through its outer covering, called a cuticle, and invade the ant’s body. The fungus then proliferates and kills its host. With tens of thousands of ants tromping around the colony, the parasitic fungus could easily spread through contact, with disastrous results.

Read the rest of the article, and watch a couple videos, at Smithsonian Insider.