Electric eels make leaping attacks

Research confirms 200-year-old story by Alexander von Humboldt

Date: June 6, 2016

Source: Vanderbilt University

In a legendary account the famous 19th century explorer and naturalist Alexander von Humboldt recounted a dramatic battle between horses and electric eels that he witnessed on a field trip to the Amazon. In the following 200 years, however, there have been no scientific reports of similar behavior on the part of the eels, suggesting that perhaps von Humboldt exaggerated.

Last year, Vanderbilt University biologist Kenneth Catania accidentally discovered that, under certain conditions, the electric eels that he has been studying will react even more dramatically than von Humboldt described: When cornered by a threatening object that is partially submerged, they will often attack by raising up out of the water, pressing their chin against the object's side and administering a series of powerful electrical shocks.

Catania, who is the Stevenson Professor of Biological Sciences, has included a description of this behavior, an assessment of its effectiveness and an explanation of the evolutionary advantages it provides the eels in the paper "Leaping eels electrify threats supporting von Humboldt's account of a battle with horses," published online this week in the Proceedings of the National Academy of Sciences early edition.

"The first time I read von Humboldt's tale, I thought it was completely bizarre," said Catania. "Why would the eels attack the horses instead of swimming away?"

The biologist keeps the eels he studies in large tanks. Initially, he used a net with metal rim and handle to transfer the eels from one place to another. "In hindsight, it probably wasn't the best design to use with electric eels," he acknowledged. However, it was a serendipitous choice. As he scooped up the larger eels he found that every so often, an eel would stop trying to evade the net and attack it by leaping out of the water while pressing its chin to the handle, all the while generating a series of high-voltage pulses. (He was wearing rubber gloves so he didn't get shocked.)

In a previous study, Catania found that eels interpret small conductors as prey. In the case of the metal-rimmed net, the eels seem to interpret the large conductor emerging from the water as a potential predator. Catania described the eel's defensive behavior as "both literally and figuratively shocking."

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