By Lisa Gonzalez
While insects from the tropics like the famous Morpho butterfly get most of the credit for their stunning iridescent colors, insects from more Mediterranean climates such as Los Angeles can also exhibit striking metallic exoskeletons. One such dazzling discovery, pictured below in all its glimmering azure glory, is a mason bee that has turned up from only 2 sites: our Museum’s Nature Garden and our LA River adjacent site in Atwater. Solitary mason bees, like their close cousin the leaf cutter bee, use materials from their environment such as mud, leaves, or flowers to line the cells where they provision and protect their young. This specimen stands out like a beacon (or a bee-con?) when surrounded by mostly dark to earth-toned specimens in the sample, which prompts the question about this little flying jewel: what’s the purpose of all this showiness?
As it turns out, the metallic suit may occur for a variety of poorly understood reasons (including warning coloration), or may just be a very aesthetically pleasing (to our eyes) by-product of the reinforced cuticle that makes up the exoskeleton. The insect’s outside structure is composed of many layers of various compounds including chitin and sclerotin that can interact with light by refracting color, resulting in what we call “structural coloration” (in contrast to color produced by pigments produced inside the body). Insects that have these brilliant shields of blues, purples or greens are protected by the extra layers of cuticle which work like a coat of armor against insect defenses, such as stings.
Take for example the cuckoo wasp, pictured below, which gets it name for its sly ability to sneak into other wasp’s nests to lay an egg, just like a cuckoo bird. Cuckoo wasps stake out other wasp’s tunneled nests, and rather than tossing the eggs in hand-grenade style, or using a long egg-laying tube as many other wasps do, enter boldly in hopes of finding the precious provisions they seek to co-opt for their offspring. If the mother wasp happens to return home at the time of the fearless break in, the cuckoo wasp rolls into a ball like a tiny armadillo and keeps its cool, knowing that the stings will not penetrate her armor.
These reinforced exoskeletons protect the insects in life, resulting in gorgeous structural coloration that gives them a bedazzling gem-like appearance long after their job on this planet is done. Specimens in our collection that date back to the beginning of the Entomology Department (101 years ago, when the museum opened!) that have this type of coloration will remain as beautiful today as they did the day they were collected.