One of the more interesting photographic experiences is exposing insects to ultraviolet light. Many insects will emit a blue-green glow when subjected to UV light, including some scorpions and millipedes. I have also seen beetles eyes that produce the same effect. No one knows exactly why some insects fluoresce under UV light, though theories abound. In any case under UV light of the frequency 320-400 nm the exoskeleton of these animals absorbs UV light and re-emits it as visible light, often blue or green. Since some insects and birds see UV light it makes me wonder what they see in each other.
Here are two species of flat-backed millipedes, one found in Florida and one in Georgia at mid-level elevations of the Appalachian Mountains. I discovered them by searching the forest floor at night using an UV flashlight and looking for anything that glowed.
As you can see, each fluoresces differently than the other. One millipede is largely brown under natural light and the legs glow in UV light. It was one of my first efforts at this type of photography. The other species is the more vivid of the two, which I photographed recently, exhibiting a stunning black and red color in natural light. It fluoresces bright blue all over with UV light.