Bombardier beetles are remarkable escape artists. They can blast their predators with their toxic chemical secretions.
The insects also have a backup plan even when they get unfortunate enough to be eaten. These creatures use the same noxious chemicals to blast their way from the inside of their predator.
Toxic Chemical Spray
The natural predator of the bombardier beetle is the Japanese common toad. Shinji Sugiura and Takuya Sato of Kobe University in Japan hypothesized that over many years of exposure, these amphibians have evolved greater tolerance to their prey's toxic chemicals than the stream toads.
In an experiment reported in the journal Biology Letters, the researchers decided to test this hypothesis. They captured bombardier beetles, which they then divided into two groups.
The insects in one group were poked with forceps so they would discharge all their toxic chemical sprays. The beetles from another group were left alone so they are still "fully loaded." All the beetles were then fed to the toads.
Researchers heard an explosion inside each of the amphibians that swallowed the fully loaded beetles. which means that the beetles ejected their chemical spray inside of the toads.
The researchers observed that the common toads vomited their prey 35 percent of the time while the stream toads ejected the insects 57 percent of the time, which support their hypothesis about the evolutionary adaptation of the toads.
Of those that ejected their defensive chemicals prior to being swallowed by the toads, only 5 percent were ejected. Most were "successfully digested."
The researchers said that this means that the boiling hot chemical spray was indeed the beetles' key to freedom. Not all of the loaded beetles survived but those that were vomited were alive and active after 20 minutes.
Larger beetles had better chances of survival. Smaller frogs were also more likely to puke.
High Tolerance For Digestive Juices
It also appears that the beetles have evolved high tolerance for the digestive juices of the frog. The beetles could survive anywhere from 12 to 107 minutes inside a toad's stomach. The researchers think that the toxic brew may neutralize the fluids and enzymes inside the toad's stomach while also causing the amphibians to vomit.
"The strong acids in the gastric juices in the predators' stomachs may kill the prey before vomiting them out. This suggests that bombardier beetle species may have evolved the ability to survive toads' digestive system," Sugiura said.