This millipede and beetle have a toxic relationship

April 29, 2019


The work of CNR alumnus Brandt Weary and Kipling Will has been featured in KQED’s Deep Look video series. The video highlights a Bay Area species called Xystocheir dissecta, a millipede that carries deadly cyanide and benzaldehyde to ward off would-be predators.

If they’re feeling threatened, these millipedes produce an invisible, odorless hydrogen cyanide gas that they spray at predators, which is virtually toxic to all organisms. One byproduct is benzaldehyde, which gives off the scent of bitter almonds, as an additional signal that they’re secreting poison.

The millipedes don’t poison themselves, however. They’ve developed an immunity.

The cyanide can kill nearly any other animal trying to dine on the millipedes. Except one.

New research has found that one tough beetle is the only known predator in the world that can survive a direct blast of cyanide gas and keep going.

Brandt Weary, who majored in Molecular Environmental Biology and graduated in 2018, studied these hardy beetles for his senior thesis, which was also supported by a SPUR grant. The beetles, known as Promecognathus crassus, love to eat millipedes, even though they are only one-fifth the millipedes’ size.

Weary wanted to know more about how the beetles withstood the millipedes’ tough chemical defense. He found that while many other beetles will avoid the cyanide-spraying millipedes, Promecognathus seeks them out.

“I'd actually put them in a dish together and watch them hunt,” he said. “The millipedes are spraying cyanide, and the beetles don't seem to mind. Then I actually tested to see if the beetles can resist cyanide. It seems that they can. It’s very unusual in the animal kingdom.”

Will, an associate professor who oversaw Weary’s study, said researchers still aren’t entirely sure how the beetles can take a blast of cyanide that would kill many other insects.

“We knew that the beetles preferred millipedes and seemed to be quite evolved to eat them, but that implies some mechanism by which they overcome or bypass nasty cyanide,” he said.

Read more about Weary and Will’s research on KQED’s website.