Epomis: the insect that eats insectivores

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"Jesus, it's like eating a soft boiled egg then having a chicken fetus carve it's way out of your gut." This seemingly suicidal beetle belongs to the genus Epomis, a group of carabid beetles from Africa, Eurasia and especially the Middle East. The lives of these beetles have remained a mystery for the most part, but three species-E. circumscriptus, E. dejeani, and E. nigricans-have made headlines because of exactly what one is shown doing in this image. These are the only predatory insects in the world to prey exclusively on vertebrates, at least as larvae. Epomis beetles are specialist amphibian hunters. The following text is based heavily on studies done by Dr. Gil Wizen and the numerous articles and blog posts detailing his observations. Note: because it is just not practical to film these animals in the wild, most of the images and videos in this article come from Dr. Wizen's lab. If this bothers you, leave.

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The larvae hunt by using themselves as bait. Waving their antennae to attract attention, they wait for an amphibian to try and eat them. As soon as they are sighted, they begin to wave their antennae faster and more radically, appearing like a prey item in distress. Some species add to this by opening and closing their jaws. The majority of terrestrial amphibians have keen sight and rely heavily on vision to hunt. They, therefore, can be easily made to focus on and attack small moving objects, a tendency that these larvae focus on. When the frog or salamander makes its ill-fated move, the larval beetle dodges the tongue, then latches onto the would-be predator's mouth or throat. https://www.youtube.com/watch?v=2ou3_q41-rc (and filmed in the wild!)

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Diagram of the amphibian-luring dance.

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Like most carabids, the larvae of Epomis beetles are armed with huge, scythe-like mandibles that snap shut and cling on tenaciously. As an extra adaptation for hunting their own predators, Epomis larvae have not one, but two points on each mandible, enabling for better grip.

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Even if the frog manages to shake the larva off, it's not over. As long as the poor vertebrate is within reach, the Epomis larva will latch onto the nearest appendage or body part of the frog, and resume the attack. Once the larva has latched on, it will begin to inject enzymes and suck liquified tissue from the amphibian, eating it alive. Video link: https://www.youtube.com/watch?v=Nm428RTPLhk

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As the eating continues, the still-alive frog is dissolved inside its own skin and sucked dry, until even the skin starts to melt.

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Eventually, only a random collection of larger bones and skin and organ fragments would be left strewn where the attack took place. But sometimes it gets worse (for the frogs).

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Of the over 400 trials done by Dr. Wizen that involved feeding amphibians to Epomis larvae, a mere seven frogs actually managed to bite and then detach the larva, and only one frog actually managed to swallow the larva. And even in that case, that wasn't the end of the story. The larva could be seen actively moving around within the amphibian's digestive tract, and it turned out that it was biting and eating the victim from the inside out. When, after two hours, the larva was disgorged, the frog became anorexic, obviously because the larva liquified and ate much of the internal organs. It then resumed its attack from the outside and finished off the frog. This may sound like hyperbole, but Dr. Wizen recorded the whole event. It can be found in the following link. NSFL! https://www.youtube.com/watch?v=0y1FPm5WNVc

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Epomis larvae will molt twice before pupating. During the first instar, when they are newly hatched, they need only one successful kill in order to gain enough nutrients to molt and grow. But by the third instar, they may need up to five victims to gain enough energy for metamorphosis. And after the metamorphosis, they keep killing frogs.

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As adults, the Epomis tactic for attacking frogs is less subtle and more dramatic: they simply stalk then attack like most predators do. The beetle will ride the amphibian around as it tries to maul it.

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An adult Epomis will bite through the muscles and tendons attached to the spine, in effect detaching the frog's legs from the rest of tis musculature. It will then proceed to gruesomely eat the struggling amphibian alive. https://www.youtube.com/watch?v=RMkFb5n97cU https://www.youtube.com/watch?v=2KiT9qbvsIE

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Salamanders aren't immune to being attacked, either.

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This predator-prey relationship is unusual for several reasons. - In most cases where prey animals start to eat their own predators, it is a simple matter of opportunity: if the normally predatory species is small due to being young, or badly outnumbered. But Epomis beetles are hunting their own predators all the time, predators that are much larger and more common than they are. - Plenty of invertebrates will eat vertebrates. Most predators operate by the rule of "if it's meat and it seems possible to kill, it's a potential target". Hence the cases of spiders catching birds and bats, among others. But these beetles eat mostly vertebrates, and in their larval stage they eat nothing but vertebrates. - Most predator-prey relationships favour the prey, or at most are equally matched. But these beetles have won all 400 of the 400 feeding attempts. Even if we discount the seven cases where the frog managed to detach itself from the beetle, that's still 393 out of 400 cases, the highest success rate for any raptorial predator. Dr. Wizen speculates that the frog-eating habits of Epomis originally evolved as a defensive adaptation. When a few beetle larvae that pushed defensive measures further turned out to have an evolutionary advantage, the tendency to attack and consume one's own predators became fixed as a predatory adaptation.

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Of course, the origins of this specialized diet doesn't make it any easier for some people to witness. As one Internet commentator has noted (http://blogs.discovermagazine.com/notrocketscience/2011/09/21/beetle-larva-lures-and-kills-frogs-while-the-adult-hunts-and-paralyses-them/) "I think, Ed, that the revolting feeling of this has more to do with the fact that it contradicts the mental order we have of Nature: it is a disturbing combination of SMALL hunting and eating BIG (instead of the opposite) and “INFERIOR” form of life -according to our way of looking at it- winning over “SUPERIOR” form of life (instead of the opposite)." "Add to that the following concepts: – “UGLY AND CRUEL” killing “CUTE AND FAMILIAR” – an unseen, slow and painful way of killing – the infallibility of the larva (100% rate of success!!), and the feeling that it is indestructible (alive and in perfect shape after 2 hours in the toad´s stomach!!) And THE RESULT IS HORROR" "(the larva, by the way, reminds me of “ALIEN, the 8th passenger”, the perfect killing machine: creepy, cruel, indestrutible, infallible, nightmarish…)" But of course, as the above commentator noted, our notions of "inferior" and "superior", or "ugly" versus 'cute", do not actually exist in nature. There is no hierarchy that dictates that vertebrates eat invertebrates, and "ugly" does not mean anything negative. The Epomis beetle does what it does simply to eat and survive. That said, being eaten alive slowly by your food seems like a horrible way to go.

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