April 17, 2022
One summer day several years ago while I was walking alone on the Desoto Upper Falls trail in north Georgia, an enormous click beetle landed on my forearm. Over two inches long with a black exterior speckled with small white spots, the beetle had two enormous black eyespots on its head. It is commonly known as the Eastern Eyed Click Beetle. There are around 10,000 species of click beetles worldwide, all distinguished by the unique ability to quickly snap their bodies. If turned on their back, they can flip themselves as much as 20 times their height into the air without using their legs and land on their feet. This jump is always accompanied by an audible click.
To perform their acrobatic feats, click beetles use something called snap-buckling, a type of instability in which an elastic object rapidly jumps from one state to another, thereby releasing energy extremely quickly. A familiar example is the little pop-up toys that are half-spheres of rubber that can be turned inside out. When you invert one and set it on a hard surface, it will eventually snap back to its natural shape and leap upwards. Snap-buckling is a basic principle in mechanical engineering and is used to generate movement in applications ranging from soft robotics to artificial heart valves. The super-fast energy release of the click beetle is produced by a hinge between its thorax and abdomen where energy is built up by the beetle’s muscles for release. The hinge has a peg on one side that stays latched to a lip on the other side of the hinge. The release of the latch produces both a click and the explosive unbending motion that causes the beetle to leap upward.
Hummingbirds, including the exquisite ruby-throated hummingbird common in the north Georgia mountains, also depend on snap-buckling in their pursuit of the flying insects which provides the protein and nutrients they need but can’t get from nectar alone. When catching insects in midair, a hummingbird’s beak snaps shut in less than a hundredth of a second—much too quickly to be explained by the action of direct jaw muscles alone. The explanation lies in the structure of the hummingbird’s beak which, unlike that of other midair insect-eating birds such as swifts and nighthawks, is made of solid bone. The downward bend of the hummingbird’s lower beak puts stress on the bone, storing elastic energy. As soon as the hummingbird’s beak is maximally bent, it springs back to its original position and snaps closed.
I caught and released the Eyed Click Beetle, but not before returning with it to the trail parking lot and photographing it in bright sunlight on a Chick-fil-A napkin retrieved from my car. I framed the photo which has hung for years on my home office wall as a reminder of my favorite forest hiking trail.