Sometimes large, land-based predators threaten to attack electric eels from above. When that happens, these eels can leap at the threat from the water, a new study finds. And upon contact, those eels can deliver high-voltage attacks to ward off the invader.
Kenneth Catania is a biologist at Vanderbilt University in Nashville, Tenn. He has been studying electric eels for years. He reports on this’ leaping behavior in the June 6 Proceedings of the National Academy of Sciences.
Catania isn’t the first scientist to describe eel leaping. In 1807, German naturalist Alexander von Humboldt reported seeing it while visiting the Amazon seven years earlier. He had hired local fishermen to collect electric eels so that he could study the animals. The fishermen led about 30 horses and mules into a muddy pond. There, eels leapt up. They pressed themselves against the large mammals, delivering mighty shocks. Eventually the eels exhausted themselves. That’s when the fishermen were able to catch five of them. But there were casualties: Two horses died.
Still, no one had reported such behavior again in the next 200 years. That’s why most scientists dismissed Humboldt’s account as a bunch of malarkey. Until, that is, Catania witnessed something odd while working with his eels. To get one out of its cage, he would reach in with a large net. That net had a metallic rim and handle. And the eels attacked. Each time, an eel would leap up, touch its chin to the metal and discharge a high-voltage volley. (Yes, Catania was smart enough to wear protective gloves.)
A MIGHTY LEAP By leaping up and striking at a predator with its chin, an electric eel can deliver a powerful shock to defend itself. VIDEO PRODUCTION: H. THOMPSON; FOOTAGE: KENNETH CATANIA/VANDERBILT UNIV.
Catania hooked meters that measure voltage and amperage to an aluminum plate. Afterward, he let the eels leap at it. The higher a leap, the more voltage and amperage an eel produced.
Indeed, getting high enough is key to effectively zapping an attacker, he now concludes. Once an eel gets high enough, the charge it delivers has no path back into the water (and the eel) except through the targeted threat. So a high leap produces a big zap.
By lacing a fake arm and a plastic alligator head with LEDs, Catania was then able to visualize the effect of this attack. The higher an eel struck the target, the more LEDs it lit up with its electric discharge.
In the wild, eels may be stuck in small, muddy ponds during the dry season. There, they don’t have any escape routes. And electrifying the water around them may not be enough to deter a large, terrestrial predator that has only a part of its body submerged. Attacking, in this case, may be the best option an eel has for defense.