Blinded by the Light

Light pollution can happen in the daytime, too—which could be disastrous for some species, according to a study in Frontiers in Ecology and the Environment. At issue are glass buildings, asphalt roads, and even oil slicks that do a surprisingly good job of mirroring the polarized light animals use to recognize bodies of water. Hundreds of species of aquatic insects, not to mention some birds, use the light for navigating to feeding and breeding grounds.

The problem is, dark and shiny man-made surfaces reflect polarized light in much the same way as water, setting what the study’s authors call an “ecological trap.” They witnessed, for example, a dragonfly so mesmerized that it mistakenly laid its eggs on a highway and then died from dehydration and exhaustion. Although the team did not study the overall scope of the problem, they speculate that it could be a widespread and serious hazard. Many aquatic insects experience complete reproductive failure when they lay eggs on artificial polarizers. But the study does offer a glimmer of hope: some simple measures, like painting white hash marks on roads, could disrupt the hypnotic effect. ❧ —Jessica Leber

Horvath, G. et al. 2009. Polarized light pollution: a new kind of ecological photopollution. Frontiers in Ecology and the Environment DOI:10.1890/080129.

Image: ©Heinerle/