These animals have evolved to escape certain death
The surprising escapes from near-death situations of beetles and other small animals illustrate how both prey and predators can adapt to challenges over time.
You might think that an insect being swallowed by a predator would mark the end of that critter’s life story. But for some, it’s no big deal. From crawling back up the digestive tract of their attacker, to releasing a burning blast from inside its belly, some resilient species have evolved creative ways to escape death—seemingly against all odds.
“It is generally assumed that once prey are eaten or taken into a predator’s mouth, death is inevitable,” says Shinji Sugiura, an ecologist at Kobe University in Japan. However, nature doesn’t always follows strict rules, and a number of small animals, from insects to eels, have evolved different strategies to escape after being eaten.
“These defenses are so surprising because they happen at a point in the sequence when all hope seems to be lost,” says Brian Gall, a zoologist at Hanover College in Indiana. “And yet, out you come to survive, feed, and breed another day! It’s weird to think about food fighting back, let alone winning. But that’s exactly what natural selection has driven some of these amazing organisms to do in the face of overwhelming defeat.”
Over the decades, researchers have managed to highlight and unveil some of these breathtaking strategies, with new escaping techniques still being discovered.
Don’t eat these beetles
Beetles seems to be at the top of the list of insects able to orchestrate the most unimaginable escapes.
Sugiura reported recently in Scientific Reports that different species of aquatic beetles are able to use their legs to make their predators spit them out.
To find that out, Sugiura conducted experiments in an aquarium. He fed the predator, the Japanese common catfish, eight different species of aquatic beetles, and documented what happened once the fish ate them.
Some beetles were completely consumed by the catfish, while others, seconds after being eaten, were spat out alive. Smaller species were more successful at escaping then others.
But how did they do it?
To reveal their hidden strategy, Sugiura conducted one additional experiment using the Japanese water scavenger beetle, which he found to be one of species that is best at making their predators spit them out. He cut the legs of some of these beetles and fed them to the catfish. In this case, the escape rate dropped from 70 percent to 15 percent. The catfish was more successful at ingesting the legless prey, suggesting that once inside the mouth, the beetles probably use their limbs to run or cling—inducing the predator to spit them out.
This isn’t the only example of legs saving aquatic beetles’ lives.
In another study published in Current Biology in 2020, Sugiura fed Japanese water scavenger beetles to five different frog species, showing that most of them managed to escape from the frog’s vents after being swallowed.
Some of the water scavenger beetle’s features probably helps its daring escape, such as a small air pocket that allows it to breathe once inside the frog, and a strong exoskeleton that protects it from the digestive juices. But in this case too, the critter’s legs seem to play a key role. Further experiments showed that the insects probably use their limbs to actively move inside the digestive tract of the frogs and escape from the vents.
Other beetles use a more “explosive” escaping strategy.
Bombardier beetles are known to literally “bomb” their predators when attacked—releasing a hot chemical spray that may reach the boiling point of water, 212 degrees Fahrenheit. However, when toads manage to swallow them, the beetles keep fighting, releasing their blast from inside the toad. This can induce the predator to regurgitate the critter. Covered in vomit, the beetle is alive and well, and can go on with its life almost as if nothing happened.
Like all predator-prey interactions, these near-death escaping abilities probably evolved in the never-ending evolutionary arm race between the predators and the prey. “If there's a small chance of survival after capture, evolution is going to try to exploit it,” says Sarah Hermann, a predator-prey ecologist at Penn State University.
Even more great escapes
Beetles aren’t the only critters that seem to cheat certain death.
Some velvet ants—which despite their name, are actually wasps—have been found to escape after being eaten by toads, resisting for up to 20 minutes inside their stomach. They escape by inducing their predator to regurgitate them before being digested.
Gordian worms, on the other hand, which are known to parasitize and manipulate host insects, can perform an even more impressive escape. When the host gets eaten, the worms can sometimes crawl up the digestive tract of their assailant. In a study published in 2006 in Nature, researchers showed that some of the worms could escape from the mouth and nose of frogs that ate their host, or from the gills of the predator fish.
Juvenile Japanese eels can actively escape from their predator after being swallowed, too. And some species of snail can apparently passively survive being eaten by birds, passing through their digestive system and then getting excreted with feces. This inconvenient process may help the gastropods disperse to areas that they wouldn’t normally reach.
While these behaviors are usually considered rare, Sugiura says they might just have been overlooked because of the difficulty of observing them in the wild, and may be therefore “more common than previously thought.”
Rethinking predators and prey
Some aspects of predators might have pushed these behaviors to appear. “I think that the ability to escape in this way is closely related to the feeding mode of the predator,” says Sugiura. These kinds of strategies, he says, may be more widespread in the prey of animals such as frogs and catfish that swallow their prey alive, instead of killing and chewing it before swallowing.
These curious abilities also challenge the linear way scientists tend to think about predator-prey interactions, says Hermann. In the classical ecology framework, a predator encounters its prey, captures it, and kills it. But great escapes like those of the aquatic beetles prove that this sequence of interactions can be far more complex, making us “rethink what it means to be eaten,” and the real impact of predators on prey, she says. They also illustrate how both prey and predators can adapt to challenges over time.
A predator is considered a "powerful organism, this one that really drives the dynamics of organisms across space and time. And what these examples give us is evidence that that is not always the case,” she adds. “Predation isn't always the end of the story. It can just be the beginning of another evolutionary battleground between predators and prey.”
