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Glowing genitalia reveal the identity of mysterious millipedes

Some arthropods are easy to tell apart. Others, not so much. Some flat-backed millipedes in the genus Pseudopolydesmus look almost identical regardless of their species, making it difficult for scientists to figure out who’s who. Now, researchers have discovered a special way to identify these insect relatives: Shine an ultraviolet (UV) light on their genitals.

Under normal light, these millipedes look unremarkable—they’re less than 2 centimeters long with brown exoskeletons. To see whether they looked different in altered lighting, a group of scientists photographed the millipedes under UV light using a special camera that produces highly detailed images. When the mug shots were done, they found that some species’s genitals glowed different colors—a dazzling variety of greens and blues, they report today in the Zoological Journal of the Linnean Society. Others simply stood out more under the UV lighting.

The source of the millipedes’ glowing genitalia is still a mystery. However, being able to tell the creatures apart without using arduous techniques like DNA analysis is an important step forward, scientists say.

*Correction, 22 April, 3:10 p.m. An earlier version of this story misidentified millipedes as insects.