Alexander von Humboldt, we’re sorry. You were right about the electric eels jumping out of the water to attack the horses.
Vanderbilt University biologist Kenneth Catania confirmed the 200-year-old “myth” is actually fact.
And not only did he film eels in the act, Catania says the process of leaving the water significantly ups the eels’ voltage.
Von Humboldt, a German naturalist and explorer of Latin America in the late 1700s and early 1800s, inadvertantly documented the behaviour more than 200 years ago, but his claims have been met with scepticism ever since.
In 1800, von Humboldt was exploring the Orinoco River when locals told him about eels in the river which could deliver a deadly shock to humans.
To catch them, they told von Humboldt to drive some wild horses into the river to scare the eels up and out of the mud.
It worked. So well in fact, several horse died, possibly due to being stunned and drowned.
Von Humboldt’s claim was backed up in the form of this sketch which was printed in The Naturalist’s Library, London in 1860:
But that was the only time any claim of “leaping electric eels” had ever been scientifically documented.
Catania, the Stevenson Professor of Biological Sciences, has a habit of studying unusual animal behaviour and publishing single-author papers on topics such as how tentacled snakes convince fish to swim into their mouths.
He turned his attention on electric eels last year. His first discovery was that eels can also send their pulses out over distances which first paralyse any fish up ahead. In order to find it, another set of pulses makes the paralysed fish pulse, giving away its position.
But he told Phys Org he was fascinated by von Humboldt’s tale.
“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 answer is the cornered eels may have simply decided offence was the best form of defence. And evolution has helped them a little on the way.
Catania’s discovery was also almost accidental. He noted that while he was scooping eels out of tanks, the odd larger one would stop trying to escape the net and instead turn to attack it.
The attacking eel would try to get as far out of the water as possible before pressing its chin to the net handle. (Catania was wearing rubber gloves.)
Again, why attack so aggressively in the first place? So, on a hunch, Catania devised a way to measure how much power the eel was delivering, using LEDs, and a voltmeter and ammeter attached to an aluminum plate.
Here’s what he saw:
The arm’s a fake but you can clearly see more electricity being delivered the further the eel climbs out of the water.
“When you see the LEDs light up, think of them as the endings of pain nerves being stimulated. That will give you an idea of how effective these attacks can be,” Catania said.
The idea behind the attack is that the shock is a circuit looping from the eel’s chin to the eel’s tail. Touch the eel in the water and its power dissipates throughout the water.
But the further the eel’s chin is out of the water, the more its current will travel through the victim until it completes the loop back into the water and the eel’s tail.
That, Catania says, maximises the shock to the victim and to a larger portion of its body.
Here it goes again with a fake alligator head:
Catania believes the defensive mechanism may have evolved to help the eels survive the dry season when rivers are lower.
You can read more about his research at Phys Org.
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