Cysteodemus wislizeni (Meloidae) Denver Museum of Nature and Science; Chris Grinter
Desert Blister Beetle
Length: 10-15 mm. Males usually smaller than the females
Why a purple butt beret?
The poofy purple butt-cover is made of the two outer wing covers of the beetle, or elytra. Chris Grinter, the collector-photographer of this beetle and Curatorial Assistant at the Denver Museum of Nature & Science said “I don’t know the function of the inflated elytra for this species; perhaps all that empty space allows a bit of extra cooling effect? That’s a wild guess, but they are seemingly well adapted for walking around at the hottest part of the day… The surface temps of desert sand can approach 175-200ºF, so they must like it hot.”
That covers why their behind might be round; but why dimply and shiny? Lots of insects are amazingly shiny, and the diversity of ways they create their shine is remarkable. Many of the brightest colored insects don’t have pigments–their colors are structural.
Close up look at the shiny beetle beret Denver Museum of Nature and Science, Chris Grinter
Insects can have three-dimensional photonic crystals shaped like diamonds. Or they might have quasi-ordered coherent scattering arrays. Mostly, insects have anexoskeleton that is made of many layers, and that laminar structure is perfectly suited for subtle refraction tweaks to make shiny shells. Many layers of chitin microfibers in a protein matrix make up the cuticle, the outer, non-living part of an insect’s shell.
What is the mechanism of this particular beetle species’ shiny behind? And why is their derrière so big? We don’t know yet. Like many things in entomology, too many beetles, too little time.
Another view of the purple fabulousness. Denver Museum of Nature and Science, Chris Grinter
a) A schematic of a multi-layer reflective insect cuticle, (b) TEM cross section of a shiny beetle cuticle (c) simple multilayer colour in a buprestid; (d) (e) (f) schematics of different arrangements of cuticle reflectors Seago et al, 2008.