Last year, Kenneth Catania, a professor of biological sciences at Vanderbilt University in Tennessee, was able to corroborate a centuries-old story about electric eels leaping out of the water to shock would-be assailants.
Prussian naturalist and explorer Alexander von Humboldt was the first to document the behaviour, all the way back in 1807. Over the next 200-plus years, however, no other scientists were ever able to observe an electric eel’s leaping abilities, and von Humboldt’s account came to be considered apocryphal by most eel researchers.
Catania published the results of a study in the Proceedings of the National Academy of Sciences in June 2016 that definitively showed electric eels can and do propel themselves out of the water in a defensive behavior that allows them to deliver their high-voltage payload directly to a target. Catania theorized that this was most advantageous to the South American natives during the Amazon’s dry season, when they can be found in small pools and are therefore at greater risk of predation.
You can watch Catania’s experiment, in which an eel in an aquarium attacks an imitation predator embedded with LEDs powered by the eel’s electric shock, in this video:
Another advantage of leaping out of the water to zap attackers is that the eel’s electrical shock doesn’t have to travel through the water first, which causes it to dissipate and therefore pack less of a punch. But just how much of a charge can eels deliver, anyway?
Catania has now answered that question, as well, in a study published in the journal Current Biology this month.
In order to study the electrical circuit created when an eel leaps from the water and presses its chin against another animal (or human, as the case may be), Catania built a contraption that allowed him to measure the strength of the electrical current as it flowed through a human arm – in this case, his own arm. For the experiment, Catania used a relatively small, juvenile eel, which meant that it would have a comparatively low shocking ability.
“Despite its small size, the juvenile eel was able to communicate 40-50 mA of current during each leap,” Catania writes in the study, adding that “the eel’s volley included more than 20 pulses, imparting 40 mA, at a rate of roughly 175 Hz.”
Forty to 50 milliamps is enough to cause a person or animal considerable pain, Catania notes: “Although 40-50 mA may not seem like much electrical current, it is far above the levels usually used to study pain and reflexive withdrawal reflexes. Most studies of withdrawal reflexes in humans stimulate with transcutaneous currents in the 5-10 mA range. Withdrawal reflexes of horse forelimbs can be elicited with transcutaneous currents ranging from 1.7 to 5.5 mA. Likewise, in dogs, withdrawal reflexes are elicited with transcutaneous currents of 2-4 mA.”
“It’s impressive that a little eel could deliver that much electricity,” Catania said in a statement. “We don’t know the main driver of the behaviour, but they need to deter predators, and I can tell you it’s really good at that. I can’t imagine an animal that had received this [jolt] sticking around.”
Roughly 3.9 Watts of power was transferred into Catania’s arm at the peak of each discharge – which the juvenile eel, had it been in the wild, would use on predators like crocodiles, cats, and “who knows what else,” according to Catania. Based on this data, he estimates that a fully grown electric eel could impart as much as 63 Watts into its target, which Catania notes is nearly an order of magnitude greater than the 7.4 Watts transferred by the pulses of the tasers used by law enforcement.
That does indeed seem like a powerful deterrent to any predator, especially when delivered directly to the predator’s body by a an eel flinging itself out of the water.
“We’ve known these animals give off a huge amount of electricity, and everybody thought that was really amazing,” Catania said. “But they aren’t just simple animals that go around shocking stuff. They’ve evolved to produce stronger and stronger electrical discharges, and in concert they’ve evolved these behaviors to more efficiently use them.”
This article first appeared on Mongabay.
