Kevin Murphy

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LED lights may disrupt the bat signal

Light-emitting diode (LED) streetlights often draw moths and other insects into small areas at night, setting a buffet for nocturnal predators, but certain aspects of the lights themselves might be rendering insects vulnerable in even more sinister ways, new research suggests. Many cities and towns are upgrading their streetlights from power-hungry gas-vapor lamps to LEDs as a cost-saving matter. In a 4-night study conducted at sites near Bristol, U.K., researchers mimicked one of these newfangled streetlights by placing an array of LEDs inside a streetlight housing on top of a 4-meter-tall tripod far from other sources of artificial light. Then they used a speaker system to broadcast the feeding calls of Nyctalus noctula, a common bat (pictured) that feeds on beetles and moths. Analyses of videos showed that only 24% of moths that heard the bat signals under the LED lights took evasive action, whereas 60% dove erratically when exposed to such chirps when the lights were off, the researchers report online today in Royal Society Open Science. The reasons aren’t clear, the researchers note, but they may stem from the broad range of wavelengths emitted by LEDs: Some moth species shut off their bat-avoiding behavior in the daytime, so the floodlit insects may be interpreting LED streetlights as daylight. Such behavioral changes, besides being potentially fatal to individual moths in the short term, may over the long term cause insect populations to drop dramatically—which in turn may decrease the food supply for furry flyers. Although some of these moths or their caterpillars are noted agricultural pests, a decline in other insects in these groups could decrease the pollination of certain plant species with nectar-rich flowers. Presumably, insects that can’t discern the ultrasonic calls of foraging bats—and therefore can’t avoid the predators—won’t be directly affected by a shift to LEDs.