

By Ed Yong | February 15, 2012 10:00 am





These grisly acts have been documented by Gil Wizen and Avital Gasith from Tel-Aviv University in Israel. Gasith discovered the beetle’s behaviour four years ago, when he found several larvae attached to frogs in the wild. Now, he and Wizen have worked out its strategy.

The larva lures amphibians by alternately waving its antennae and moving its jaws, moving faster and faster as its prey draws closer. The movements exploit the fact that amphibians run on simple hunting programmes: pay attention to moving objects; attack small ones; and avoid large ones. The small, waving larva certainly falls within the definition of ‘prey’; the amphibian approaches and attacks.

Its tongue is fast, taking just a tenth of a second to launch and extend. The larva is faster. Before it’s caught, it grabs the amphibian’s face and, after repositioning itself in a more suitable place, starts to eat. At first, it behaves like a parasite, sucking the bodily fluids of its prey. Then, those mandibles come into play and it starts to chew. Eventually, only bones remain.


The larva develops in three phases and it kills a new victim during each one. Once it eats its fill, it finds a hiding place, sloughs off its hard skin, expands its body and lures in a new amphibian to fuel the next stage of its growth.

As adults, the beetles often share the same moist shelters as amphibians during the day, only to prey upon them at night. In the wild, Wizen and Gasith found three beetles munching on toads from behind. In the lab, they saw that the beetle bites an amphibian in the back, hanging on like a rodeo jockey as its furiously jumping victim tries to dislodge it. The beetle makes an incision in its prey’s back with its jaws. Within a few minutes, it is paralysed. Within a few hours, it is nothing but a head and limbs.

The beetle’s cut doesn’t harm the amphibian’s spine. “I believe that the beetle damages the connecting muscles of the amphibian’s rear legs, thus preventing it from jumping away and escaping,” says Wizen. “This hypothesis still needs to be confirmed.”

Prey animals sometimes turn the tables on their predators, but that’s often because they’re bigger at some stage of their lives, because they suddenly outnumber their enemies. The Epomis beetles are unusual in three ways: they are much smaller than the amphibians they hunt; their role-reversal is compulsory since the larvae only eat amphibians; and they have evolved a behaviour that lures in their prey.

Clearly, frogs and salamanders haven’t learned that Epomis larvae are dangerous predators in their own right. That may be because the beetles are relatively rare, compared to the vast variety of ground beetles that amphibians regularly eat. Indeed, Wizen and Gasith found that the droppings of local frogs often contain the carcasses of other related beetles.

Only a few species of Epomis have turned the tables, transforming from prey into predators. Indeed, Wizen and Gasith think that the beetle’s behaviour first evolved as a form of defence. While other insects protect themselves with poison, camouflage, or aggressiveness, Epomis beetles rely on offence as the best defence.

Reference: Wizen & Gasith. 2011. An Unprecedented Role Reversal: Ground Beetle Larvae (Coleoptera: Carabidae) Lure Amphibians and Prey upon Them. PLoS ONE

Wizen & Gasith. 2011. Predation of amphibians by carabid beetles of the genus Epomis found in the central coastal plain of Israel.

Images and videos all courtesy of Gil Wizen


Comments (2)

  1. mfumbesi

    [QUOTE]……killed and ate the animal that had just eaten it[/QUOTE]
    Lord, I’m going to have nightmares.

  2. Nick Waters

    They sacrificed 382 amphibians to demonstrate this unique foraging strategy. That seems rather excessive…


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