The Legless Amphibian That Eats Its Mother’s Skin

That’s no earthworm—it’s a vertebrate, specifically a kind of amphibian called a caecilian. But you can call it an earthworm if you want. I’m not gonna stop you.

Perhaps the most contentious title out there is “World’s Greatest Mom.” My mother probably thinks she is, but so too does her mother, and I think they could both make pretty strong cases. But the sacrifices that human moms make pale in comparison to what’s going on in nature. There’s a bug, for instance, whose young devour their mother from the inside out. And one species of deep-sea octopus looks after her eggs for an incredible four and a half years, then perishes.

One amphibian, though, goes about things a little more creepily: A caecilian (pronounced suh-SILL-ee-in) momma lets her kids eat her skin. Like, a lot of it. They’ve even got specialized baby teeth to more efficiently strip her skin away.

That alone is enough to win the caecilian a spot in this column, but pretty much everything about the caecilian is goofy. First of all, they have no legs, not even vestigial traces of limbs (they look just like that giant space slug that almost ate the Millennium Falcon in Star Wars—in fact I’d be surprised if the monster wasn’t inspired by caecilians). They reproduce in pretty much every way imaginable. Et cetera, et cetera.

The 200 or so species of caecilians range from just a few inches long to over 3 feet, and they live in tropical habitats all over the world, rummaging around in the leaf litter or burrowing or even taking to the water. Many species have tiny eyes, or their eye sockets are covered with bone, since peepers don’t do you no good nohow when you’re underground. It makes more sense for the structure to atrophy away over evolutionary time—an eye that isn’t there can’t get infected. Same goes for the legs. It takes a whole lot of valuable time and energy and resources to build those things.

So what caecilians are sensing their world with instead of eyes is “a so-called tentacle, which is usually in front of the eye, but behind the nostrils,” says zoologist Thomas Kleinteich of Germany’s Kiel University. “So this is chemosensory reception. They can actually smell their environment and use this when they are burrowing in the ground.”

When it comes to sex, caecilians have opted for some serious diversification. Some species lay eggs, while others give birth to live young, while still other aquatic varieties go through a larval stage. That’s pretty impressive when you consider that there’s only 200 species of caecilians. Compare this to the thousands upon thousands of species of frog, which typically go with the lay-eggs-add-sperm-develop-into-a-tadpole strategy, though there are a few exceptions.

As far as looking after the young goes—and caecilians all seem to do this to some degree—they have a couple of options for feeding. If you’re laying big eggs, you can pack a lot of yolk in there for them to feed on, then stand guard as they develop. Or…well, this brings us back to the skin thing. “What some species do is actually they have less yolk in the eggs,” says Kleinteich, “and then the juveniles hatch at a premature stage. They don’t actually catch prey, so the first thing they eat is, they scrape off the skin of the females.”

And here you were thinking I was a dum-dum for suggesting the space worm from Star Wars had to have been inspired by the caecilians. You can keep thinking I’m a dum-dum for plenty of other reasons, though.

Other scientists described this approach rather dramatically in a 2008 paper. “Feeding behaviour is quite frenetic with the young frequently tearing pieces of skin by spinning along their long axes and sometimes struggling over the same piece of skin. The mother remains calm during this activity. When the mother has been peeled, the young continue to search for and eat fragments of skin on the substrate.”

The female caecilian’s skin is uniquely adapted to handle being a smorgasbord. Breeding females’ skin is packed with energy-rich lipids (fatty acids), and is constantly replaced so the juveniles have a steady source of food. The frantic feeding event takes only 7 minutes, but just a day and a half later, the skin has regrown and the young can chow down once again. Adorably, juvenile caecilians have baby teeth just like us, only theirs look a bit like shovels—shovels that dig out their mother’s skin.

Not to be outdone, in species where the young develop within their mother, they’ll…gnaw on her uterus. This “stimulates the aggregation of what’s called uterine milk,” says Kleinteich. “Basically, the female keeps producing uterus epithelial cells, which are then scraped off by the developing fetuses in the uterus.” Charming.

This Ichthyophis sp. is one weird-looking bumblebee.

As caecilians mature, though, they lose those baby teeth and grow extremely sharp, conical chompers and become opportunistic hunters. Small varieties probably snap up insects and earthworms (scientists don’t know much about their diets), while bigger species can tackle fish and other amphibians. They’re not the speediest of predators, but they’re voracious.

Caecilians themselves look quite tasty, on account of essentially being squirming tubes of flesh. So some of them have gone and evolved toxic mucus on their skin. And in case you were considering getting one for a roommate, some are apparently so toxic that they’ve reportedly killed other creatures they’ve shared tanks with. “There’s glands in the skin of course for mucus production to keep the skin wet,” says Kleinteich, “but there’s also glands in the skin for toxins and antibiotics to keep bacteria and fungi away.”

Read more at Wired Science