In an explosive burst, it swam up the handle of the net, partially leaving the water and heading straight for Catania’s hand. Pressing its chin against the handle, it delivered its trademark shocks—rapid trains of 600-volt pulses that can stun small fish and incapacitate humans (or horses). “Despite wearing a [rubber] glove, it was pretty intimidating,” says Catania. “I made a little note to myself to come back and study this.”
Over time, Catania got better at eel-wrangling. In the last two years, he has single-handedly shown that an electric eel—not a true eel, but a type of knifefish—is a battery, Taser, remote control, and tracking device, all in one. With different kinds of pulses, it can make a prey animal twitch and so give away its presence, it can paralyze its victim by forcing all its muscles to contract, and it can monitor the movements of the stiffened targets. And when it wants to take down a really big target, like a crayfish, it can curl its body to deliver twice the shock for no extra effort.
Through all these discoveries, Catania’s mind kept returning to that image of a cornered eel hurtling up his net. “I suddenly realized how effective it would be as a defensive strategy,” he says.
The electric eel is a living battery, with the positive pole at its head and the negative one at its tail. When it’s fully submerged, the current it creates passes every which way through the water in between. That’s great for killing a small submerged target, but terrible for shocking a larger standing predator like a wading bird or English physicist Michael Faraday, who, after some (quite literally) hands-on experiments with electric eels in 1838, wrote: “When one hand was in the water the shock was felt in that hand only, whatever part of the fish it was applied to; it was not very strong, and it was only in the part immersed in water.”
But when the eel leaves the water and presses its head against its foe, it creates a short circuit. There’s nowhere else for the current to go except through the target. “At its full height, it’s giving virtually all of the current to the potential threat,” says Catania. “What it’s doing parallels a dimmer switch or a volume control knob,” he adds. By jumping, it dials its shocks up to 11.
“It’s a welcome example of a serendipitous discovery in animal behavior,” says Graciela Unguez from the New Mexico State University. “It pays off to be attentive to the unexpected!”
At first, Catania measured the eel’s volleys using conducting rods hooked up to a voltmeter. But as he says, “I strive to show people as much of the behaviour as possible, and when you have an animal who’s generating hundreds of volts of electricity, you have some fun options.” Such as: embedding LEDs in a prop crocodile head and a prosthetic arm. You can see the results below.
“Each of those flashes represents the firing of the nerves in a potential predator,” says Catania. “In each of those volleys, there are 200 pulses per second. That’s a very good rate for causing pain.”