In addition to their ability to change the colors, it appears that some chameleons can also glow in the dark.

A study published in Scientific Reports found that some chameleon species from Madagascar and the African continent, particularly those from humid and forested areas, have bony protuberance along their heads that glow under ultraviolet (UV) light. The glow is visible even through their scales.

"It has long been known that bones fluoresce under UV light, but that animals use this phenomenon to fluoresce themselves has surprised us and was previously unknown," Frank Glaw, curator of Herpetology at the Bavarian State Collection of Zoology said in a statement released by Ludwig Maximilian University of Munich regarding the study.

Light 'em up

This collection of photos shows fluorescent bones in different species of chameleons This collection of photos shows fluorescent bones in different species of chameleons. (Photo: Scientific Reports)

That the bones are so clearly visible in UV shouldn't be surprising. Our teeth light up under a black light, and we can even unearth fossils this way. And fluorescence in animals isn't anything new, either. Plenty of sea creatures glow in the darkest depths of ocean, but it's not so common in land-based animals. That these chameleons light up like this demonstrates there's some value to it for these color-shifting lizards, especially since they can see UV light.

Researchers collected 160 specimens of 31 species of Calumma chameleons and conducted fluorescent and UV photography, shining lamps on the chameleons to see where they would glow.

They also analyzed their scales and skin to determine why the bony bumps were so visible and bright. It turns out that the skin around these protuberances is so thin and transparent that it creates a "window" to the bone. This thin layer of skin also seems to function as a kind of "optical filter," which skews the glow to a particular color.

"We could hardly believe our eyes when we illuminated the chameleons in our collection with a UV lamp, and almost all species showed blue, previously invisible patterns on the head, some even over the whole body," lead author of the study David Prötzel said in the university statement.

The color blue is significant because it pops against the greens and browns of the forest. This, in turn, may help the males — who exhibit more of these glowing bony protuberances on their heads than females — indicate their sexual features in a way that doesn't compromise their camouflage.

While the sample size the researchers used was small, they suspect future research will not only strengthen their findings but also create an interest in locating more glowing land-based vertebrates.

Chameleons add glow-in-the-dark bones to long list of cool traits
We know chameleons change their colors, but we didn't know they glow in the dark, too!