This Teeny Frog Makes Its Own Insect Repellent

Albertina Pimentel Lima
Albertina Pimentel Lima / Albertina Pimentel Lima

Harry Potter’s invisibility cloak was cool. But J.K. Rowling, take note: There’s a frog in South America that may have a specialized cloak that renders its wearer invisible to aggressive jerks. Scientists say the Amazonian amphibian produces a compound that shields it from detection by its ant neighbors. A report on the frog’s chemical camouflage was published in the journal Behavioral Ecology and Sociobiology [PDF].

Lithodytes lineatus is petite, maxing out at under 2 inches from nose to rear end. It makes its home throughout the Amazon rain forest under logs, near pools, and in piles of leaf litter, and it rarely lives alone. Leaf litter is pretty desirable real estate for certain populations of ants.

Sarefo via Wikimedia Commons // CC BY-SA 3.0

Those ants are impressive in their own right. The leaf-cutters (genus Atta) live an agrarian lifestyle, growing edible fungus on a mulch they make from leaf clippings. But this doesn’t make them pacifists. Animals that blunder into leaf-cutter territory live to regret it—if they live that long, because the ant attacks can be deadly.

That is, animals other than our striped frog friend, which somehow manages to live among the leaf-cutters unmolested. To find out how this was possible, a team of researchers tested the frogs, their skin, and four related species against an onslaught of ants.

In the first experiment, each frog was left in an open-mouthed glass container near a leaf-cutter ant nest. After 10 minutes, the researchers removed the frog from the arena and counted the number of ants on its skin. Each round was timed, from the moment the frog entered the container to the first ant bite.

The researchers suspected that L. lineatus was using the ants’ own pheromones against them, manufacturing a knock-off brand of ant smells from the skin in order to become "invisible." To test that hypothesis, they created an extract of frog skin. They then collected 20 unrelated frogs from the very porous species Rhinella major and gave them all a bath. Half of the frogs were bathed in L. lineatus skin extract, the rest in pure water. Then, all of them were set down by the ants’ nest, back in the battle dome.

The invisibility-cloak-via-chemical-fraud theory appears to have some merit. The first experiment exposed 10 adult L. lineatus specimens to an ants’ nest, but none of them were bitten—nor were any of the R. major specimens bathed in their skin juice. Frogs from other species, including those doused in plain water, were far less fortunate. 
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