"The camphor beetle skates on the water's surface, spreading its legs out wide and using the water's surface tension to prevent it submerging. Lots of beetles do this, but the camphor beetle has evolved a unique technique to avoid predators. When alarmed, it releases a chemical from its back legs that reduces the water surface tension. In this way, the water surface tension on the front pulls it forwards. It shoots forwards on its front feet, which are held out like skis, and steers itself by flexing its abdomen. This tiny beetle is the size of a rice grain but can travel nearly 1m a second in this way. It doesn't hunt on water, but at the water's edge, and saves this trick to escape predators." Guardian.

How does this work exactly? Why should reducing the water surface tension behind it propel it forwards? Is the pull of the water on the beetle the same as the net force of attraction that pulls the hairs of the brush together when out of the water?

Chris G

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