If you want to see some sex, violence and blackmail, don’t bother with soap operas – try looking at the surface of your local lake or stream. There, you’ll find small insects called water striders (or pond skaters), skimming across the water on outstretched legs. These legs can pick up the vibrations of prey, predators and mates, but they can also produce vibrations by tapping the water surface. And males use this ability to blackmail their way into sex. It’s a drama of sexual tension played out across the surface tension.
Water strider sex begins unceremoniously: the male mounts the female without any courtship rituals or foreplay. She may resist but if she does, he starts to actively strum the water surface with his legs. Each vibration risks attracting the attention of a hungry predator, like a fish or backswimmer (above). And because the female is underneath, she will bear the brunt of any assault. By creating dangerous vibes, the male intimidates the female into submitting to his advances. Faint heart, it is said, never did win fair lady.
Two males red-eyed tree frogs square off over a female. Fisticuffs will soon ensue and as a final challenge to each other, the males… er… vigorously shake their bums at each other. Their quivering buttocks shake the plants they sit on, sending threatening vibrations towards their rival. This secret line of communication has just been uncovered by Michael Caldwell from Boston University. To decipher these messages, he has used a hi-tech combination of infrared cameras, saplings rigged with accelerometers and even a cybernetic Robofrog.