Speedy water skimming beetles

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The Stenus rove beetles are truly blessed in bizarre adaptations. If telescopic mouthparts weren’t enough (see last post), they also have one of the most impressive defences in the animal kingdom. Often, these beetles are found in waterside habitats, where they wander about on the ground and in the vegetation shooting their spiky mouthparts out at anything that looks at them in the wrong way. Their small size and long legs means they can also take to the water and scull along as if they were walking – their weight supported by the water’s meniscus. This in itself is not all that impressive – there are lots of animals that walk on water, including lizards and even mammals (if you believe some of the stories).

If danger threatens while they’re on the water, these beetles emit an oily combination of alkaloids known as stenusin from the pygidial glands at the tip of their abdomen. This substance is so hydrophobic that as it hits the water it spreads with such force that the beetle is propelled forward at terrific speed, well, relatively. The velocity the beetle reaches is equivalent to 600-900 km/h in human terms and it does this in a fraction of a second –acceleration that would turn you or I inside out. Needless to say, any small predator will be completely bamboozled by the sudden disappearance of its dinner.

Unfortunately, there’s no photos of this as it all happens rather quickly.

There’s more about these beetles in the book, Extraordinary Animals

Further reading

Schildknecht, H. et al. (1976b). Defense chemistry of Stenus comma (Coleoptera: Staphylinidae) LXI. J. Chem. Ecol. 2: 1-11.

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