Midsummer is when meadows abound in wildlife. For weeks I have been awaiting the arrival of one of the most gorgeous of all insects Chrysocus auratus. This beetle has no accepted common name, but it is often referred to as the dogbane beetle due to its habit of feeding almost exclusively on plants in the genus Apocynum, herbaceous plants we refer to as dogbane. Dogbane grows along roadsides and trails near the forest edge. It is a perennial with clusters of small white flowers. If you damage a leaf or stem, it oozes a white sticky sap.
A pair of Chrysocus auratus in beetle bliss.
The scientific name Chrysocus auratus is derived from the Latin root that means “made of gold” and obviously refers to the fantastic metallic hues of blue, green, gold, and red on surface of the beetle. It is a wonder that an insect so conspicuous can survive in a world where birds, toads, and mice dine on insects with gusto. Herein lies the secret of the dogbane beetle. The dogbane plant, like its relative the milkweed, is full of highly poisonous compounds known as cardenolides. These compounds are toxic to a variety of animals, including humans. Cardenolides are also known as cardiac glycosides and they can have profound and lethal effects on the heart if ingested. It is likely that these compounds evolved to keep leaf-munching animals from eating dogbane. The clever Chrysocus has the ability to eat the leaves of dogbane and not be poisoned. Instead it ingests the cardiac glycosides, stores them in glands, and then secretes them when threatened by its own predators. It is believed that these toxic compounds confer protection from hungry predators that would otherwise devour Chrysocus. The conspicuous color and tendency for the beetle to feed and rest in full sight of its enemies are probably the beetle's way of advertising its nasty chemical defense. The biological message is this: “That's right, I'm bad, don't even think of eating me.” Don your boots, tuck your pants into your socks, and go into the meadow to find dogbane. You may be rewarded with a glimpse of the dogbane beetle, one of nature's most golden delights.
References
For more information on Chrysocus auratus visit the following website:
http://www.ipm.iastate.edu/ipm/icm/2003/7-28-2003/dogbane.html