This Toad Isn’t Eating a Bug. The Bug Is Eating It

What's the matter, vicious beetle larva got your tongue?

Let me get real about amphibians: The things are cocky. They’re so much bigger than their helpless prey—things like worms and insects—that they tend to indiscriminately snatch up anything that’s a manageable size.

But like the Mighty Ducks rose up to defeat the seemingly unbeatable Team Iceland, one beetle has evolved to put amphibians in their place. As larvae, beetles of the genus Epomis actually entice frogs and toads and salamanders to attack them, then whip around and sink their huge, hooked jaws into the attackers, slowly draining the life out of them. When the larvae transform into adult beetles, they get right back to it, only now they dispatch amphibians even more brutally. Like, a kind of brutality that involves snipping a frog’s leg muscles so it can’t escape.

Imagine, if you will, that you’re a toad. You’re hopping along when something catches your eye: a beetle larva shifting its jaws and antennae back and forth. Your brain tells you that anything that moves and that’s small enough for you to overpower is probably food.

So it’s decided. As you draw closer to your victim, its movements get more rapid. You draw closer still, and strike.

One of two things is going to happen at this point, neither of which will end—how should I say—well for you. You’ll get the larva in your mouth and it’ll sink its jaws into your tongue, or the larva will get you somewhere on your skin—your lips or throat or flank. The larva is just too fast for you, and may be so smooth that it can repel that famous tongue of yours.

The second outcome, though, is you manage to swallow it. Not that that will do you any good. Scientists once watched a toad nab and successfully swallow a Epomis larva, only to throw it up two hours later. At first the larva lay motionless, but then suddenly it snapped out of it and attacked the toad again.

So … you’re screwed. That larva ain’t about to let go. In fact, it starts digesting your tissue. But strangely, none of your blood is coming out, and indeed “when you slice a larva open you don’t see it full of red blood,” says Gil Wizen, an entomologist at the University of Toronto. What’s probably going on here, Wizen reckons, is the larva is secreting enzymes onto the toad to melt its flesh. “So you can say that the digestion is already beginning before the food enters the mouth,” he says.

Those double hooked jaws sink into amphibian flesh and don’t let go. How’s that for attachment issues.

All the while, you go about the life of a toad. You take a swim and gobble up insects. You will not, however, turn into a prince, because after two days, you’re so weakened you can no longer move. It’s at this point that the larva enters what Wizen calls “the predation stage.”

The larva begins chewing more, says Wizen, “and what we see is that it sort of tears tissues from the amphibian’s body. After a few hours the amphibian is reduced to just a pile of bones and just a little bit of skin.”

But this was no crime of passion. The larva is more like a serial killer. Over the course of its development, it can take down as many as nine toads, frogs, newts, or salamanders. It’s got such an appetite because it goes through three phases, known as instars, in which it needs ever more food. During the first instar, when it’s relatively small, it’ll take down just one victim. In the second instar, though, it’s two or three. In the last, as many as five.

And like a serial killer, its methods grow ever more complex as it matures. The adult beetle ups its game into some seriously sadistic stuff. While it isn’t as picky an eater as the larva, feeding on worms and other insects and even injured rodents and birds, it too loves it an amphibian.

The adult beetle doesn’t lure the victim like the larva, but instead goes full-tilt rodeo with it, jumping on a toad’s rear and sinking its jaws into the flesh. These jaws are different, though. “The jaws of the larva are hooked, modified to lock onto the amphibian’s skin,” says Wizen, “whereas with the [adults], they have serrated jaws.” The adult’s mouthparts aren’t modified to hold on tight, so it has to work fast.

The beetle has jumped onto the rear of the toad for a reason. Once the victim stops bucking, the beetle makes a small incision on the lower back. “We don’t think they damage the spine of the amphibian,” Wizen says. “But what we do think—we still need to confirm this—is that they cut the connecting muscles [of the legs] so the amphibian doesn’t have any way to escape.”

With the bronco incapacitated for good, the beetle can take its time gnawing on the victim alive. When it fills up, it trots off. If the toad isn’t yet dead, something like a bird or mammal will happily finish it off.

The whole weird circus defies belief—and bends the rules of nature. In only around 10 percent of cases is a predator smaller than its prey. Beyond that, the relationship between the Epomis beetle and its amphibian victims may in fact be unprecedented (as far as science knows). Wizen and his colleagues cite only one other case in which a prey becomes the predator: A scientist in the ’80s transferred rock lobsters, which eat snails known as whelks, to an environment with an abnormally large population of the prey, which flipped and became the predators. But that was human meddling. Epomis has evolved over millennia to turn amphibians—the eternal enemies of insects—into prey.

The relationship also resists definition. While Epomis is certainly predatory, it’s also in a way parasitic. As a larva, it doesn’t necessarily kill its victims, sometimes filling up enough and just dropping off (indeed, Wizen has collected toads with the tell-tale scars of an attack). And as I mentioned earlier, adults also don’t necessarily kill their victims either. So Epomis seems to be a kind of predator-parasite hybrid.

Read more at Wired Science