The Aquatic Menace That Gives the Worst Hickeys Ever

Lampreys are best known for their dashing blue eyes.

To quote the great Austin Powers, when provided floss to escape being lowered into a tank of ill-tempered sea bass: “OK, I get it. I have bad teeth.” Sure, it’s easy to stereotype the British for shunning American advances in oral hygiene. But it’s time to set our dental differences aside and celebrate the most ghastly mouth on Earth, which swims in the rivers of both nations, uniting us in toothy horrors.

Say hello to the lamprey, an ancient eel-like critter that’s the bane of many a river system, latching onto fish like trout and draining their blood or scraping away their flesh right down to the bone. In the Great Lakes of North America they’re an invasive menace, wreaking havoc on fisheries that tend to rely on their catches not having giant hickeys.

But all the while, let’s give respect where respect is due. This is an animal that has gone 360 million years almost totally unchanged, a brilliant parasite that’s evolved a remarkably efficient—and disturbing—means of survival.

The Scrapes of Wrath

There are three kinds of lamprey: the flesh-eaters, the blood-suckers, and the ones that quite frankly don’t do much at all. These last individuals spend anywhere from 3 to 7 years in a larval stage, and live only 6 months once they metamorphose into adults. During this time they don’t need to feed, only existing to reproduce and die (there are worse fates, I suppose).

The other two populations, though, are where things get interesting. The flesh-eaters and blood-suckers may not look like they have all that different mouths, but to a trained professional like lamprey taxonomist Claude Renaud of the Canadian Museum of Nature, the dental specializations of the two groups are quite clear.

In the center of all those impressive hooked teeth, lampreys have a structure analogous to a tongue, epically called a piston, which bears three sharp chompers, two that move side to side and another that moves up and down. This piston, according to Renaud, “has kind of a convex structure with a very strong middle tooth that’s very large, and that’s the one that permits the lamprey that feeds on flesh to remove—gouging out—a piece of flesh.”

The seven holes behind a lamprey’s eyes are its strangely round gills. If a lamprey thinks these will at all distract from its ridiculous mouth, it’s got another thing coming.

This middle tooth of the flesh-eaters is shaped like a U, in contrast to that of the blood-suckers, which looks like a W. The latter group has “finer teeth, all of them about the same size,” said Renaud. “So this W actually acts as a rasping organ instead of a gouging organ, so that permits it to kind of scrape all the tissue to get to the blood vessels.”

And another key difference between the two groups lies within the critters’ bodies. The blood-suckers have to keep that blood flowing, so they have glands in their throat that secrete an anticoagulant into the oral disk, as their mouth is not-so-seductively known. The flesh-eaters have these as well, but they’re far smaller—they’re after meat, not blood.

No matter its manner of feeding, the lamprey has to of course first find its prey, using cells along its body that help it sense vibrations in water. Once it identifies and closes in on the prey, it switches to visual cues to actually pinpoint a specific spot on the unfortunate host.

“If they’re flesh-feeders they will preferentially go for the [top] of the fish, because that’s where the most flesh is,” said Renaud. “Whereas if they’re a blood-feeder they’ll go for the underside of the fish, because that’s where they’ll get the greatest blood supply.”

A migrating salmon with a rather unwelcome passenger. Lampreys, if you were curious, are real backseat drivers.

And once they hit their target, there’s not much that can dislodge them, probably not even tickling them, though I don’t think that’s really been tested. Not only do those multitudinous hooked teeth sink deep into the flesh (Renaud will find fish with scars that are so defined that he can identify the offending species of lamprey based on the imprint’s dentition), but the lamprey also uses suction to stick to its host.

Running along the edge of the oral disk are two rings of structures. “One of them is called oral fimbriae, these are little structures that look a little bit like leaves, little flaps of tissue,” said Renaud. “And those are the ones that can adhere closely to the skin and make a really good seal.” (A nice little bit of convergent evolution here, that is, two unrelated species arriving at the same adaptation independently: The clingfish has modified fins on its belly that utilize similar structures to create a suction so strong that it can support 300 times its own weight.)

The other ring around the lamprey’s oral disk is made of conical structures known as papillae, which the creature uses to sense where best to attach to the fish. These are so sensitive that the vampiric varieties of lamprey can even use them to feel out underlying blood vessels.

“Excuse us, but do you have a moment to talk about our lord and savior Jesus Christ? Hello?”

Once the lamprey is firmly attached, it’ll stay stuck for anywhere from a few hours to a full day, rasping or gouging, then resting for a bit, then back to rasping or gouging. The blood-suckers will typically leave their prey alive after the whole ordeal, “because it’s not advantageous for a parasite, if you wish, to kill its host, because then it won’t have the ability to feed on that one again,” said Renaud. “And the host can recover, replenish its blood supply, and remain there for another meal.” Still, some die of resulting infections.

The flesh-eaters, though, laugh in the face of such mercy. They’re typically targeting smaller schooling fish like herring, boring and boring until “they’ll actually skeletonize the fish that they’re feeding on,” according to Renaud. The fish either dies from massive blood loss or infection or, you know, just having a big hole in its body.

Pissing Off America and Canada, and Other Lamprey Pursuits

Luckily for its hosts, the lamprey spends less than half of its life as a menacing adult, maybe 3 out of its 7 years. The rest of the time is spent in a rather laid-back larval stage on river bottoms, dug into the sand and detritus with their heads poking out. In this way the blind young simply wait for their food to come to them, microorganisms like plankton and algae, gathering it all in their squishy horseshoe-shaped mouths (which of course metamorphose into the fearsome maws of adulthood). The food enters a sort of filtering system of branching structures, where it gets entangled in a mucus strand that then enters the gut.

Strangely enough, it’s actually these fairly helpless larval lampreys that lead the adults to optimal spawning grounds. “The larvae can produce a pheromone that will disperse into the water system,” said Renaud. “And the adults, when they want to go to spawn, will pick up that through their nose, and are able to go and spawn where it’s great larval habitat. So it’s like the babies tell the prospective parents, ‘This is a great place to spawn, because we’re thriving.’”

A larval lamprey. Notice the mouth is fleshy instead of being positively packed with teeth. Give it time, though, and it’ll develop nice chompers. Wait … actually. Yeah … this one’s dead.

This is quite different from salmon, which when spawning famously return to the exact spot they were born, as if terribly homesick. But that spot may not necessarily be as ideal that year as when they themselves called it home. Alternatively, the lampreys, under the direction of their larval comrades, can guarantee more ideal conditions for the development of their young.

This success is nice and all—unless you’re a wildlife official around the Great Lakes. Here the U.S. and Canada are battling the invasive blood-sucking sea lamprey, which can split its time between saltwater and freshwater. Accidentally introduced here in the early 20th century, this species has proved to be an absolute fiend. Before the lampreys showed up, the Great Lakes trout fishery produced 15 million pounds a year. In the early ‘60s, after the lampreys were well established in the area, one annual catch totaled a mere 300,000 pounds. So while not as destructive as the flesh-eating variety, these blood-suckers inflict more than their fair share of lethally infectious wounds.

Fish always look surprised, so it’s hard to tell if this one is in pain or if that’s just its normal face. Actually, we can be pretty sure it’s in a good amount of pain. Anyway, lamprey bites can lead to deadly infections, potentially crashing certain fisheries.

And boy have officials struggled to keep the sea lamprey at bay. Beginning in the late ’50s, at first they tried trapping them, and then containing them with electrical barriers. Nowadays, though, scientists are looking into more clever measures.

One idea is to use the lamprey larva’s come-spawn-over-here pheromone against the species, dumping it in strategic spots in a river system, then scooping up the hoodwinked adults. Even more cunningly, scientists have been sterilizing captured males and releasing them back into the wild. That may seem silly, what with it being easier to just kill them, but in their competition to mate, these males will necessarily muscle out some of the fertile lampreys, reducing the spawning success rate. Still another campaign has used lampricides that lure larvae out of their burrows and eventually kill them.

With these efforts, the U.S. and Canada have been able to cut sea lamprey populations in some parts of the Great Lakes by 95 percent. But, Renaud notes, that remaining 5 percent will rapidly replenish the population if left unchecked. And with a dizzying network of streams and rivers in the area, some spots can’t be treated more than once every few years. “So we can never eradicate sea lamprey, but we can control it,” Renaud said. “That’s why it’s called sea lamprey control instead of sea lamprey eradication.”

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