In the 1997 movie Anaconda, there are, to put it mildly, a few scientific inaccuracies. Chief among them: Anacondas do not regurgitate their still-living prey to experience the thrill of a second kill, as the movie’s snake does with Jon Voight. They will sometimes puke up a meal, but since they constrict their victims before swallowing, the expelled individual would be very much dead.
But some animals can travel down a predator’s gullet and return to tell the tale. Consider the bombardier beetles. There are 500 species of them, named for their ability to spray scalding, caustic liquid from their backsides. They do so by mixing chemicals housed in two separate glands. Separately, these substances are inert. Together, they react with explosive results. The beetles can create around 500 of these explosions every second, creating chemical streams that reach over 100 degrees Celsius and travel at up to 22 miles per hour.
That’s enough to ward off most predators. But toads can project their sticky tongues so quickly that they can snag a bombardier beetle before it gets a chance to unleash hell. That’s certainly what Shinji Sugiura and Takuya Sato from Kobe University saw when they put the two animals together. The toads would swallow the beetles.
“However,” the duo write, “an explosion was audible inside each toad.”
And also, like, in my mind.
The beetles may have been taken by surprise, but they still managed to unleash their payloads from inside their attackers’ stomachs. The chemicals were never fatal, but they were unpleasant enough to force many of the toads to regurgitate the beetles. Toads have no gag reflex, though, so they can’t vomit in the same way that we can. Their only option is to turn their stomachs inside-out—a process that takes around 45 minutes.
It’s not that the beetles are toxic in their own right. If Sugiura and Sato forced them to exhaust their defensive sprays by provoking them with forceps, before offering them to the toads, almost all of them were eaten and digested. The beetles must also have adaptations that allow them to survive for 45 minutes inside a toad’s stomach, smothered in acidic mucus. You can see one of them ignominiously crawling away to freedom in the video below. Most of these liberated beetles can live for at least two more weeks after their escape.
There are many stories of animals that have successfully broken out of a predator’s digestive tract (although tales of humans doing so have been disputed). In 2012, on an expedition to East Timor, Mark O’ Shea picked up a rock to prop open the door of his laboratory. Beneath the rock was a common Asian toad. And wriggling out of the toad’s rear end was a Brahminy blind snake—a tiny serpent that looks like an earthworm. After presumably being swallowed (perhaps because of its wormlike appearance), it somehow crawled through the toad’s entire gut, like some kind of serpentine Andy Dufresne.
“When the toad hopped to escape, the blind snake was carried along with it,” O’Shea wrote. He eventually captured the two and separated them. The snake survived for several hours, but died overnight.
With a habit of stowing away in flowerpots, Brahminy blind snakes have become the most widespread snake on the planet. As far as we know, their native range doesn’t usually include toad butts, but O’ Shea suspects that they might be uniquely qualified to survive in such an unusual locale. After all, they’re burrowers—well-adapted to dark, constrictive, oxygen-poor environments, with tightly interlaced scales that could ward off, say, a toad’s digestive acids.
Horsehair worms probably have their own adaptations against being swallowed. They are mind-controlling parasites that infect crickets, derange them, and drive them to suicidally leap into water. Once the insects have drowned, the worms wriggle out. But Fleur Ponton from Macquarie University found that even when the crickets are eaten by a fish or a frog, which happens often, the horsehair worms can still escape from the guts of their host’s predator.
These fantastic voyages are mostly accidents, but some animals seem to benefit from being eaten. Many snails can survive being eaten by birds. This ability allows them to travel over long distances, and probably explains why genetically identical populations have been found on different Japanese islands, or on different sides of the Americas. Even though “land snails have very limited powers of active dispersal,” as Jasna Simonová dryly noted, they can cross continents by boarding feathered airliners—a possibility that Darwin suggested, and that scientists have recently confirmed.
Finally, swallowed animals can sometimes turn the tables on their swallowers in truly dramatic fashion. Gil Wizen and Avital Gasith found one such example by studying Epomis beetles. These insects eat frogs, and nothing else. When a frog lashes out with its tongue, an Epomis larva will dodge. It then grabs its attacker’s face with a pair of hooked jaws, and slowly eats the poor frog alive. Over 400 such standoffs, Wizen and Gasith saw that the beetle always won. In one case, a toad actually managed to snag an Epomis larva and swallow it. Two hours later, it regurgitated the beetle, which then turned around and ate the animal that had just eaten it.