Why is a mushroom growing on a frog? Scientists don't know, but it sure looks weird

In a bizarre, never-before-seen case, a live frog was found in India with a mushroom growing from its skin, leaving scientists puzzled.

The frog — identified as Rao's intermediate golden-backed frog (Hylarana intermedia) — was spotted sitting among 40 other individuals from the same species, perched on a twig with a white stalk and gray cap protruding out of its left flank.

The discovery was made by Lohit Y.T., a river and wetlands specialist at World Wildlife Fund (WWF) India during an expedition with friends to find reptiles and amphibians in the foothills of the Kudremukh ranges in India.

After the team shared photos of the frog, mycologists said the mushroom could be from the genus Mycena. Lohit and his co-author Chinmay C Maliye documented their discovery in a new study, published Jan. 28 in the journal Reptiles and Amphibians.

The group didn't collect the frog, and it is not known whether the fungus grew from within the frog's body or on the skin surface. Some mycologists suspect the amphibian picked up the fungus following an infection or wound — leaving a pitted area that the fungus could cling to.

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"I would guess that this is a purely superficial skin infection with Mycena, those can be sustained over a long time, [the same] as most fungal skin infections in humans," Christoffer Bugge Harder, a researcher in the University of Copenhagen's Department of Biology, who was not involved in the study, told Forbes about the new finding.

The fungus did not seem to be harming the frog, according to the study, and it had no other visible injuries.

This is not the first time amphibians have encountered fungi. Previous research revealed that amphibians are vulnerable to a pathogenic fungi called Batrachochytrium dendrobatidis, which causes the lethal skin disease chytridiomycosis. The disease is responsible for mass mortalities of amphibians across the world. Because of this, scientists wonder whether this new discovery of fungal infection could be a cause for concern.

Rao's intermediate golden-backed frogs are around the size of a thumb and are native to the Western Ghats, a mountain range running parallel to India's west coast. 

Species in the genus Mycena, meanwhile, are commonly called bonnet mushrooms. Most of these species thrive on nutrients from dead or decaying organic matter and are usually found growing in clusters on decayed wood.

Mushrooms develop in nutrient-rich places from fungal spores. The spores reproduce into thin, branching filaments, and mushrooms then grow if nutrients are available. Although most Mycena species are found on dead materials, a study published in 2023 reported growth of a Mycena species on live plants. 

Harder, who was lead author of the 2023 study, said this study suggests these mushrooms are in the process of an evolutionary development and can be invaders of living plants under favorable conditions, but that live frogs are definitely not ordinary terrain.