Posted by: Rob Viens | May 17, 2012

“Click” Goes the Beetle

May 17th found more rain falling in Rio. Darwin, the constant naturalist, took the opportunity to measure it, writing:

“Heavy rain; in the course of the day 1·6 inches fell. — as the storm passed over the Caucovado the sound produced by the drops pattering on the countless number of leaves was very singular. — It might be heard for ¼ of a mile. — I jumped up to see what it was; for it sounded like the rushing of a large body of water.” (May 17)

What a wonderful sound – falling rain.  I love to be in a tent or in the forest and hear the sound of the rain on the trees that Darwin captures so well. For more on rain in Rio, see Torrents of Rain in Rio, but for now the sounds (and Darwin’s “jumping”) remind me of another beetle – the click beetle – so it’s time to return to:

Beetle Mania logo

Like so many  beetles, the click beetle (from the Family Elateriadae) has its own unique and marvelous set of adaptations. One in particular (the one that gives them their name) is the “clicking” mechanism located between the head and the thorax.  This mechanism can snap or click in such a way that it causes the beetle to be flung into the air – helping it to escape predators, or flip over if it is stuck on its back. The snap creates a clicking sound, too.

Eyed click beetle Alaus oculatus (from Wikipedia Commons):

Alaus oculatus

In a way, the way the clicking mechanism works is sort of like the children’s game “Ant in Your Pants”, in which you press down on little plastic ants causing them to elastically rebound and fling themselves into the air (towards the pants, of course).  Click beetles don’t use exactly the same mechanism, but it is similar. (For clarification I should point out that ants are not even closely related to click beetles – they are in a completely different order of insects –the Order Hymenoptera. A more scientifically  accurate version of the game might be called “Elateriadae in Your Pants” or maybe “Click Beetles in Your Pants”, but I suppose that may not market as well.)

Watch (and hear about) a click beetle in action (from Kansas Wildlife and Parks):

Some click beetles – such as those in the Pyrophorus genus – are bioluminescent.  One species from Brazil – Pyrophorus nyctophanus – has larvae that live in termite mounds and use their glow to attract prey at night (like little “bug zappers”).  Others species use the glow to frighten predators. For example, the click beetle in the video below (posted to YouTube by hnbbs) has two glowing spots that look like large menacing eyes.

Darwin’s only comment in his Zoological Notebook about Elateriadae in the Rio de Janeiro region was:

“most of species very small” (Zoological Notebook)

That comment doesn’t do justice to Elateriadae, which consist of over 9000 species found around the world. Keep in mind that means there is about 2 click beetle species for every one mammal species on Earth! Something to ponder for the night…(RJV)


  1. Wow!! Thanks for the education about beetles, Rob. I enjoyed watching the videos. Evolution is truly a piece of art!

    • It sure is – as always Darwin says it best – “endless forms most beautiful” – they truly are!

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