Why Do Poison Dart Frogs ‘Tap Dance’ With Their Toes? Research Sheds Light on Feeding Time Footwork

Scientists observed frogs tapping their toes up to 500 times per minute when prey was present, suggesting the behavior is related to predation

Two green and black poison dart frogs sit next to each other, both facing inward, on brownish soil
Two green and black poison dart frogs Pavel Kirillov via Flickr under CC BY 2.0

The animal kingdom has no shortage of dance moves, from flamingoes’ synchronized sashays to the waltzes of scorpions. But none are quite like the tap dancing that scientists have observed in poison dart frogs: These amphibians reserve their moves not for potential mates, but for prey.

Across many of the nearly 200 species of poison dart frogs worldwide, researchers have long witnessed individuals rapidly tap the middle toes of their hind feet—sometimes up to 500 times per minute—when prey was present. But they have never quite understood why.

Now, two biologists from the University of Illinois Urbana-Champaign (UIUC) say they’re closer to an answer. After conducting a series of experiments with the Dyeing poison dart frog, published as a preprint paper earlier this year on the site bioRxiv, they suggest the vibrations from the frogs’ footwork cause insects to react and move around.

“Frogs can only really forage when prey is alive and moving,” Eva Fischer, co-author of the study and a biologist at UIUC, tells New Scientist’s Chen Ly. “So maybe this tapping could be vibrationally startling the flies and making them move.”

Tap Dancing Frogs: Posterior Toe Tapping and Feeding Behavior

Fischer and her colleague Thomas Parrish, also a biologist at UIUC, filmed 22 Dyeing poison dart frogs in their enclosures, which had a variety of natural groundcover, including leaves, soil and rocks. When feeding time came, they placed half a teaspoon of live fruit flies—one of the frogs’ favorite snacks—into the terrarium in front of them.

High-speed videos showed that the presence of food correlated with foot speed: The amphibians tapped their toes an average of 389 times per minute when the flies were present, as opposed to 50 times per minute when not.

Sometimes, the researchers placed the flies in closed petri dishes in front of the frogs, making them visible yet inaccessible. Even though the frogs tried to catch the out-of-reach prey, they tapped their toes at the slower rate of about 50 times per minute, suggesting the animals only increase their tap rate when they could feasibly capture prey.

Finally, the researchers found a significant difference in tap rate when the frogs were placed on different surfaces, with food present and available in front of them. They averaged 255 taps per minute when standing on leaves, as opposed to 98 taps per minute on soil, 118 taps per minute on agar gel and 64 taps per minute on glass.

Because leaves carry vibrations better than the other substrates, this behavior might suggest that the frogs are encouraging their prey to move around. The researchers also noticed that the frogs with higher tap rates tried to strike the flies more frequently—though higher tap rates did not necessarily correlate with higher hunting success. The findings have not yet undergone peer review.

A black and yellow poison dart frog sits on brown-grey rocks, its hind legs bent and facing away from the viewer
A yellow-banded poison dart frog. Leszek Leszczynski via Flickr under CC BY 2.0

But another recent study about poison dart frogs’ footwork, published in November in the journal Evolutionary Ecology, corroborated some of the new conclusions. Researchers at the University of Magdalena in Colombia found that 37 percent of the time, the frogs they studied accelerated their toe tapping when about to strike. This was especially true, they noted, for frogs with the longest middle toes.

“It’s a potentially really interesting example of a predator using sensory cues to manipulate prey behavior—at least there’s that possibility,” Reginald Cocroft, a biologist at the University of Missouri who collaborated on the November study, tells the New York Times’ Elizabeth Landau.

Perhaps the toe-tapping is a form of deception meant to attract prey, like the way an angler fish lures its meals with light, researchers suggest. Alternatively, says Lisa Schulte, a biologist at Goethe University in Frankfurt who co-authored a similar study last spring, toe-tapping could be a frog’s way of confirming its potential meal is truly prey.

“If a fruit fly crawls, you can see the frog get excited and look at it,” Schulte, who was not involved in either of the newer studies, told Psychology Today’s Mary Bates last May. “Then it just sits there and stares at the fruit fly until it moves again, and only when it moves again does the frog take it. My theory is that by toe-tapping, the frog might trigger the fruit fly to move again so that it can be sure the fly is a prey item that they want to eat.”

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