One of the many things I love about Charles Darwin is that he loved to collect beetles as a young man. My own passion was for bees, from the time I was around five. I’d collect as many as I could in a jar, sometimes two dozen or more, buzzing around inside my Mason jar with air holes hammered into the lid. I’d stare at them for an hour or so—hornets, wasps, yellow jackets, honeybees, bumblebees—and then I’d let them go. There was an art to that—I’d unscrew the lid so it was just barely on, fling the jar into the bushes, and high tail it the other way. I never got stung.

So according to his autobiography, one day when Charles was a student at Cambridge (1828 – 31), he went out to collect beetles. He tore some bark off a tree and found two rare species, seizing one in each hand. But “then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth.”

A natural inclination for anyone, right? Where else would you stash a live bug, but in your mouth?

“Alas it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as well as the third one.”

According to this website, the third beetle has since been identified as the Crucifix Ground Beetle (Panagaeus cruxmajor).

Darwin didn’t identify what species from the family Carabus it was that ejected the burning fluid inside his mouth. It may have been a bombardier beetle; some species can emit an acrid gas with a loud popping sound.