I post a BYGL Alert each year about Dogbane Beetles (Chrysochus auratus) because the beetle's light-blending artistry makes it one of the most beautiful beetles found in Ohio. Enjoying these shimmering living gems on their namesake host is the entomology equivalent to "stop and smell the roses."
The beetle's scientific name, Chrysochus auratus, loosely translates to "made of gold." In fact, gold is only one of a medley of colors displayed by these gorgeous native beetles. As you change your viewing angle, the beetles glisten with mixed shades of green, copper, blue, red, and of course gold.
The secret to the myriad display of colors is found just below the surface of the beetle's exoskeleton. Beneath an outer translucent layer rests stacks of tiny slanting plates that cover color pigments. Light rays striking the surface of the plates are reflected as a shimmering sheen, while light rays that bounce off the pigments produce various colors. The result is a lustrous mix of ever-changing hews; a kaleidoscope of colors that are almost unmatched in the insect world.
Of course, the beetle's colorful display isn't meant to elicit "oohs and ahhs" from humans; it's meant to signal, "don't mess with me" to predators. Using bright colors to send a warning message to enemies is known as "aposematic coloration."
Dogbane (Apocynum spp.) is the representative species for the dogbane family, Apocynaceae, which includes milkweeds and other plants that ooze sticky white sap ladened with poisonous alkaloids (cardiac glycosides). Indeed, the genus name Apocynum translates to "poisonous to dogs," or "dog killer." Sap from dogbane is reported to have been used at one time against ravenous feral dogs.
Dogbane beetles feed on the three dogbanes found in North America: common or hemp dogbane (A. cannabinum), fly-trap or spreading dogbane (A. androsaemifolium), and intermediate dogbane (Apocynum × floribundum). Although there are reports in the literature that the beetle feeds on various milkweeds (Asclepias spp.), I've scoured milkweeds in Ohio without finding this beetle. I've wondered if perhaps the reports are actually referring to the Cobalt or Blue Milkweed Beetle (C. cobaltinus) that does feed on western milkweeds. However, this beetle has not been reported in Ohio.
Dogbane beetles ingest the poisonous cardiac glycosides in dogbane sap, store the chemicals in specialized glands, and then they secrete the noxious chemical brew when threatened by predators. Their bright coloration advertises their nasty chemical defense strategy.
So, get out and look for dogbane beetles while enjoying the heat! If you find them, experience the kaleidoscope of colors by viewing the same beetle at different angles to the sun. They are eye candy … but don't eat them.