A chance discovery, which confirms 200-year-old claims of eels attacking horses in the Amazon, has proved that electric eels leap out of water to attack predators.
Never corner an animal, always leave them an out. A cat will swipe its claws at you, a dog might bite. An eel, in the stuff of nightmares, will leap out of the water, reach as high up as it can and deliver a powerful electric shock.
The latter was discovered by Vanderbilt University biologist Kenneth Catania, who was transferring eels from one tank to another, using a net with an ill-advised metal rim.
Most eels struggled to swim away from the net but, on occasion, they would stop, turn and leap out to touch the frame of the net.
Eels interpret small conductors as prey, now it seems they see large conductors as predators.
The metal rim of the net (“In hindsight, it probably wasn’t the best design to use with electric eels,” said Catania) acts as this predator, something which confirms a legendary account of the famous 19th century explorer and naturalist Alexander von Humboldt.
Around 200 years ago, he recounted a dramatic battle between horses and electric eels that he witnessed on a field trip to the Amazon – with no evidence of it since occurring, it edged towards myth, away from truth.
Now, though, he’s been vindicated.
“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?”
Once he noticed the behaviour he tried approaching the eels with non-conducting materials, which they largely ignore – living things typically conduct electricity.
When a partially submerged conducting ‘body’ approached, though, they struck. Interestingly, the higher they leapt out of the water, the stronger the electric shock.
That’s because it shocks directly from its chin onto the target – rather than spread throughout the water when fully submerged.
Then the electric current travels through the target until it can exit back into the water where it travels back to the eel’s tail, completing the circuit.
“This allow the eels to deliver shocks with a maximum amount of power to partially-submerged land animals that invade their territory,” Catania said. “It also allows them to electrify a much larger portion of the invader’s body.”
Catania, whose study appears in the journal Proceedings of the National Academy of Sciences, described the eel’s defensive behaviour as “both literally and figuratively shocking”.