The Epomis beetle

So you happen to find that you have suddenly turned into an toad.  Not only that, but instead of being at your computer you seem to have been transported to the coastal plains of Israel.  Normally you might find this to be a slightly unusual set of circumstances.  But you are now a toad, and toads, as a general rule, are not known for their mental prowess.  So instead of having a mental breakdown at the discovery of being transformed into an amphibian, you go about your new life as if it is all you have ever known.

Before long you come across a beetle larvae that looks rather tasty.  As you approach it in hopes of getting your munch on, it starts waving its antennae and mandibles at you.  Your instincts to attempt to eat anything small and twitchy kick in and you are drawn towards what is sure to be a succulent meal.

The closer you get the faster and more frantically the little morsel waves about.  At this point, you cannot resist and pounce on the beetle larvae and just as your tongue darts out to grab your first meal as a toad, the larvae quickly dodges your attack and sinks its mandibles into your soft flesh.

Somewhere in the back of your toad mind, you realize that this shouldn't be.  You are the predator.  Insects are merely crunchy snacks to the likes of you.  Yet despite this, you can't ignore the fact that what you thought was to be your meal is now feeding on you.

You feel your blood being drained as you flail about frantically trying to dislodge your attacker.  As you begin to weaken, a glimmer of hope returns to your tiny brain as you feel the larvae dislodging itself from you.  Could you have finally fought off the surprise attack?

As you attempt to crawl away, the larvae repositions itself on your back and bites down with surgical precision.  You feel its sharp mandibles biting through the muscles of your back, leaving you effectively paralyzed.  Whatever hope you had is now gone as the reality of your situation sinks in.  You are about to be eaten alive.

Now that you can no longer fight, the larvae can eat at its leisure until there is nothing left but a pile of bones that used to be your new toad self.

Had you not been transformed into a toad, you might have realized that the flailing of antennae and mandibles was a cunning ploy of the beetles and their larvae of the genus Epomis.  These beetles, whose relatives are all preyed upon by amphibians, have turned the tables upon their once predator.  Using the instincts of amphibians against them, Epomis beetles actively prey on any and all amphibians that still believe themselves to be the predator.

The larvae feed exclusively upon amphibians, while the adults feed on a variety of prey items, including amphibians.  When observed, the beetle or its larvae win the match close to 100% of the time.  Even after being eaten, the beetle or larvae will thrash about until the amphibian is forced to regurgitate it.  The beetle, seemingly unharmed, will start feeding on the would be predator right away.  Even after staying in the stomach for two hours, the beetle will not be beaten and once regurgitated, will attack its choice prey item.

Epomis is the only known natural instance of a prey item using its one time placement as a predated upon species as a means to evolve into the predator.  Since the beetle wins essentially every match it finds itself in, there is little hope for the amphibians to evolve a proper counter, nor are the beetles numerous enough to damage amphibian populations significantly.  Thus leaving the species of Epomis in what is sure to be a rather comfortable position as one of the most unexpected of predators.

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References:
Wizen G, & Gasith A (2011). An unprecedented role reversal: ground beetle larvae (Coleoptera: Carabidae) lure amphibians and prey upon them. PloS one, 6 (9) PMID: 21957480
Read the original paper.