When you're a kid, it's easy to take things for granted—to assume, for example, that your experiences, however unique, are relatively common. But then you find out way later in life that no, in fact not everyone tested the "Mary Poppins Theory of Gravity" by jumping off their hay barn clutching an umbrella, as I did, or was sung to sleep each night by the high-pitched bugling of the neighborhood elk herd.
That sense of distinction is how I felt reading the news that a researcher at Vanderbilt University had finally corroborated a centuries-old tale about electric eels. I thought: People don't know this already?
This month, Kenneth Catania, a scientist with a passion for studying Electrophorus electricus, reported in the Proceedings of the National Academy of Sciences a peculiar behavior among electric eels: When confronted with a large object in their aquarium (like a net, a plastic hand, or, in one experiment, an LED-embedded alligator head), the eels flung themselves out of the water, climbing up the objects and pressing into them with their chins, for lack of a better word, discharging a volley of high-voltage shocks along the way—kind of like slimy, spring-loaded tasers.
This was the same story that Prussian explorer Alexander von Humboldt returned with after traveling in South America in the early 1800s. In an attempt to study electricity, Humboldt conscripted some locals to drive a herd of horses into a shallow pond known to contain a population of eels.1 A violent confrontation ensued where, according to Humboldt, the eels reared out of the water and pressed themselves against the terrified animals' legs (two horses died, presumably from shock and drowning). And until Catania noticed the eels in his lab doing something similar, nobody else had seen, or reported seeing, such behavior in the 200-plus years since Humboldt published his account.
Well, nobody except me. I have seen an electric eel jump out of the water. And so did my 8th-grade classmates at Valders Middle School, in Valders, Wisconsin, in the spring of 2000.
It was after lunch. Mr. Jerale, our wiry, severely countenanced science teacher, was lecturing at the board in the front of the classroom—something about sedimentary rock formation. Fluffy, his three foot-long electric eel, was in its usual spot: a massive glass tank on a counter in the back of the room. Most of our interactions with Fluffy up until that point consisted of watching his weekly feeding; waiting for the moment when a buckets' worth of alewives all stopped swimming mid fin-stroke and froze, floating belly up, before being sucked through Fluffy's underbite. That was about as exciting as it got.
Fluffy's body retracted powerfully into a thick coil before launching out of the tank.
Until this one day—sedimentary rock day—when the tank was undergoing some maintenance. It had been emptied earlier in the morning and was now being refilled. I noticed that the water was much higher in the tank than it usually was—Mr. Jerale seemed to have forgotten to turn off the hose. And Fluffy was now nosing around at the place where the tank cover had been moved aside to accommodate it.
As I stared at this new development I caught the eye of Sarah, a girl with round glasses and big hair who sat alone in the very back row. She began to turn around to see what I was looking at, and in that instant, Fluffy's body retracted powerfully into a thick coil before launching out of the tank, hurtling over Sarah and landing with a thunderous smack on the tiled floor.
The tank lid clattered to the counter. Sarah screamed and scrambled up on to her worktable. Fluffy was now writhing between the metal legs of her upturned chair, apparently attempting to find a target for its discharge. Mr. Jerale sprang toward his supply closet, pulling on rubber gloves that ran up past his elbows and barking orders at everyone to stay calm and exit the classroom.
We filed out the door and ran around the building to watch from the windows of our first-floor classroom. Mr. Jerale had by now found a large cardboard box and was cautiously trying to corral Fluffy into it, who did not seem interested in going quietly back to captivity. At one point the box started to tear under the weight (and wriggling) of the massive fish, but not before Fluffy was finally returned to the tank and the top safely reinstalled.
When I related this event to Catania, he said, "I've never actually seen them try to leap out of their tanks. I'm going to guess that's pretty strange. But that's why when I did start to see this regular occurrence of them jumping up and interacting with my net in this directed way, that it was particularly surprising."
When I asked what sorts of animals threaten electric eels in the wild (other than herds of ill-fated horses), Catania said we really don't have a good answer for that. It turns out there's still a lot we don't know about them. But other researchers in the field have seen land-based predators and local fishermen take advantage of the dry season when pools and rivers shrink and the eels are more vulnerable. And Catania did find that his eels most often attacked when the water in the aquarium was lowered. "The higher the eel gets, the more current is forced through the potential threat," he said.
Catania's series of voltage recording experiments offer an explanation for how this self-defense behavior evolved in the first place.
"That leaping behavior is not likely to just emerge suddenly. Instead you can see how maybe the eel first just got a little bit closer, and that was effective and was selected for," he said. "Touching the threat would be another increment. Getting out of water would be the next one. Each stage would increase the experienced pulse effect of the eel's high voltage output, providing a successive advantage."
So maybe Fluffy felt threatened when his tank got emptied, and panicked. Or, maybe, he just got bored.
1. Despite the name, electric eels are not actually eels. They're a species of freshwater-dwelling knifefish that breathe air and can produce up to 860 volts of electricity at a time.
Megan Molteni is a freelance science writer, producer, and researcher based (mostly) in Minneapolis. She tweets about fish and frisbee @MeganMolteni.
The lead photograph is courtesy of brownpau via Flickr.