On their travels in search of new dung, these beetles seem to land and take off quite a few times. They are relatively tolerant of being photographed (!), but after a few moments, seem to tire of the attentions of a large hominid, and spread their wings and take flight! I managed to catch some of the different stages of the elytra-opening and wing-unfolding process in different individuals.The wings (hind wings really) are stored, folded up under the wing cases, called elytra. These hard wing cases protect the more delicate wings whilst the beetles are on the ground, feeding or pushing their way through dung in this case! Wings do not unfold instantly of course! Here is one (below) just starting to open its elytra. The initial stages of opening the wing cases are relatively slow, and there is a slight delay as the wings are extended, but once the wings are wide open and expanded, the beetle takes flight almost immediately. There are no muscles in the wing itself, and the extension of the hind wings of beetles probably occurs as a result of the hydraulic pressure of blood (haemolymph), being pumped into veins in the wings. The system of unfolding (and folding) is highly complex, with folding occurring along flexion lines. The extension of the wing also involves contraction of muscles at the base of the wing, located in the thorax, together with an increase of blood pressure (Sun et al., 2014). When the wings are folded away, they occupy a much smaller area than when open and extended of course. I think these beetles take off without jumping off the ground! In conclusion, deploying wings in beetles and other insects is a remarkable engineering feat and has been the focus of many detailed studies. Understanding how insects such as this fold and unfold their wings, from a single point at the base of the wing, could provide many useful solutions to engineering problems. In the words of one researcher:
“the hind wings of the Coleoptera are an example of a smart structure: a remote motor, stiff plates and elastic rods create a defined and repeatable movement” (Haas, 2000).
On a final note, these beetles are I believe, at risk of poisoning from ivermectins, veterinary pharmaceuticals given to cows to treat roundworms and other stomach parasites. I was very alarmed to come across a whole group of dead or dying beetles, all lying on the ground not far from each other (below). There was no dung in the vicinity; it was as though they all succumbed at the same time. The fact that not all of them were dead, and some were moribund and still twitching, made me suspect poisoning. Very worrying and something I plan to investigate further.
References and further reading
Haas, F. (2000). Wing folding in insects: A natural, deployable structure. In IUTAM-IASS Symposium on Deployable Structures: Theory and Applications (pp. 137-142). Springer, Dordrecht.
Sun, J., Ling, M., Wu, W., Bhushan, B., & Tong, J. (2014). The hydraulic mechanism of the unfolding of hind wings in Dorcus titanus platymelus (order: Coleoptera). International journal of molecular sciences, 15(4), 6009-6018.