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Dragonfly Death Traps


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When Iraqi forces finally pulled out of Kuwait in 1991, they left in their wake hundreds of blown-up oil wells and pipelines. Much of the spilled oil still pollutes the Kuwaiti desert, in the form of oil lakes and ponds. These oil lakes have proved to be a death trap for water-seeking insects like dragonflies. The reason: To insects, oil looks more like water than water itself. Biophysicist Gábor Horváth of the University of Tübingen in Germany and his colleague Jochen Zeil, a biologist then at Kuwait University and now at the Australian National University, studied how the oil pools reflect light. Light reflecting from both water and oil is partially polarized--that is, the light waves reflecting from these liquids vibrate at a distinct angle. Insects, unlike humans, can see polarized light and use it to find water. In fact, says Horváth, the oil surface is more polarized than the water surface, and therefore oil is more attractive to insects. He has found that oil can trap 25 times more dragonflies than water. A small oil pond could trap thousands of dragonflies when they are swarming, Horváth says, and nobody has studied yet what impact that would have on the insect population.

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