By Douglas Quenqua, FEB. 6, 2018,
Photo by Dr. Shinji Sugiura, et
al., Kobe University.
For most prey, the game is over
once they’ve been swallowed. But one species of beetle can escape from a toad’s
stomach nearly two hours after being eaten, according to a new study.
Found in wooded areas on nearly
every continent, bombardier beetles — a group that consists of more than 500
species — get their name from their signature defense mechanism: When
threatened, they shoot a hot chemical spray from their rear end. In Japan, the
insects have long been known as, “the farting bug.”
Toads have been observed vomiting
bombardier beetles after eating them, but no one knew exactly why, or how long
the beetles survived after their brush with digestion.
To better understand the beetle’s
defenses, two biologists from Kobe University fed a species of bombardier
beetle to two different species of toad collected from forests in central
Japan. One toad species shared its natural habitat with that particular species
of beetle, while the other was unlikely to encounter it in the wild.
After the beetles were swallowed,
a small explosion could be heard inside each toad, indicating that the insects
were firing their defenses. Overall, 43 percent of the toads vomited the
beetles, taking anywhere from 12 to 107 minutes.
Most important (at least to the
insects): Despite being covered in mucus, meaning they had entered the toads’
digestive system, every evicted beetle was still alive, and all but one
survived for another two weeks. No toads died on account of eating the beetles.
“It surprised us that the beetles
vomited by toads were still alive and active,” said Shinji Sugiura, an author
of the study, which was published Tuesday in the journal Biology Letters.
But some toads were better able
to digest the beetles than others. Only 35 percent of the toads that shared
habitat with the beetles coughed them up, compared to 57 percent of the toads
with no common habitat. The findings suggest that regular exposure to
bombardier beetles has allowed some toads to evolve a tolerance to their
poison.
Size mattered, too. Large beetles
escaped more frequently than small beetles, and small toads were more likely to
vomit beetles than large toads. The reason, presumably, is that large beetles
are able to produce more poison, and smaller toads are less able to tolerate
it, said Dr. Sugiura.
To be sure that the beetles were
using their spray to escape, the researchers also fed the toads beetles that
had been forced to expel their poison just before being consumed. Nearly all of
those beetles were successfully digested.
The authors say it’s still not
clear whether the beetles have evolved a resistance to a toad’s digestive
fluids and enzymes, which may have helped them survive their ordeal inside a
toad’s belly. That may be the case, but it’s also possible that their poison
spray prevented the toads from producing enough digestive juices to harm them.
Bombardier beetles are not the
only creatures that can shoot toxic liquids. Fire ants, spitting cobras and
even some species of birds are known to disable their prey with harmful sprays.
Based on the current study, Dr.
Sugiura predicted that other spraying species may also be able to escape from a
predator’s stomach. “Well-defended species that force some predators to vomit
will be found in other animal groups,” he said. Consider yourselves warned,
predators.
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