In my wanderings among the woods and fields I often encounter beetles, which are not usually considered among the most colorful of the insects, as are the butterflies. However there are some striking exceptions to this rule, one of which I call the “jewel of the forest,” the six-spotted tiger beetle. This little gem is an iridescent green of the most amazing hue (see photo, left) which is accentuated by its habitat in sunny gaps in the forest. These little monsters are truly tigers at their scale and rum amok among the tiny insect denizens of the forest floor. Although I will be quick to point out the adaptive advantages of many color patterns, I am at a loss to provide any definitive answer for this distinctive green flash. Obviously it makes the beetle more visible to predators with color vision (birds), but the speed and alertness of this tiny tiger may negate this factor. Indeed it might even confuse a predator since the green wing covers are lifted during flight. The color is not a sexual attractor since both sexes are green. So we are left with another of nature’s many mysteries.
Another impressively colored beetle is the dogbane beetle (see photo, center) which has an amazingly iridescent “coat of many colors.” Such rainbow-like patterns are normally produced by a series of tiny grooves that diffract light, not by pigments. This beetle feeds on dogbane which is a close relative of milkweed and has a similarly milky and toxic sap. So it is likely that this beetle is advertising a toxicity derived from its food. Such an advertisement is common among a group of insects that feed on milkweed, including the red milkweed or four-eyed beetle (shown here mating- and note the double eye- hence the scientific name Tetraopes tetrophthalmus – photo right). Isn’t it interesting how birds recognize that red-orange advertises toxicity in insects, but that red fruits are ripe and yummy?
So while you are out and about in nature watch for those very numerous beetles (the most species diverse of any kinds of animals) and contemplate the purposes, not to mention the beauty, of the many different colors and patterns that they possess.
Bill Dunson, Englewood, FL & Galax, VA