ÐÓ°ÉÔ­´´

Q: While working in the garden, I saw a beetle walk past, take a wrong step
and land on its back. Without my intervention it would have stayed in this
position and probably died. Why is it that millions of years of evolution have
not eradicated this basic and potentially lethal design fault?

A: If your correspondent had left the beetle in place on its back it
probably would not have remained as it was until death. Beetles and other
insects have a variety of mechanisms which they can use for righting
themselves in these circumstances which, as the writer presumes correctly,
must arise often and hazardously.

The most famous mechanism is used by the click beetles (Elateridae), which
are able to launch themselves into the air by the sudden release of a blunt
spine which is kept under pressure in a specialised groove on the venter.

As many readers will have noticed, the click beetle often makes several
attempts before it lands on its feet but its success, given time, is
assured.

Other less sophisticated beetle correcting mechanisms include spreading the
wings, reaching out with the legs, and rocking the body in a forward-aft or
side-to-side motion.

Any readers wanting to learn more about the subject should see the
following paper: Comparative righting behaviour of insects, J. T. Chao, Chung
Hsing University, Taiwan, 1985. I can supply the author’s address to any
interested readers.

A: Only a minority of beetles possess a body plan that poses such a
problem. For example, I have worked with several species of ladybeetle
(Coccinellidae) in the laboratory, and most are able to right themselves with
relative ease.

The species that do find themselves stranded on their backs tend to be the
larger varieties that possess strongly convex elytra (the first pair of
hardened, protective wings).

Ladybeetles that do become stranded on a smooth surface will eventually
unfold their membranous hind wings, which are normally hidden beneath the
elytra, and then use these to right themselves. Part of the answer then, is
that very few species become stranded and those that do eventually flip
themselves over by means of their hind wings.

Over the long course of evolution it was probably quite rare for beetles
developing in temperate forests and grasslands to encounter totally smooth
surfaces or bare soil that was devoid of plant litter. Under normal
circumstances, grass blades, fallen leaves and plant stems would offer a
convenient hold for beetles that happened to become overturned.

The reduced rate of predation and numerous other benefits that are
conferred by a hard protective covering, which far outweighs the occasional
stranding, has contributed to the enormous evolutionary succes of beetles. In
terms of both absolute numbers and numbers of species, beetles are the most
successful group of animals on the planet.

A: I doubt whether the beetle was a healthy specimen that just happened to
fall over and was unable to right itself. It is more likely that it was an
old, sick or diseased specimen that was nearing the end of its life. When this
happens in beetles, they lose a great deal of their mobility and coordination
and they become very unstable when walking. They frequently fall over when
placed on a hard flat surface and are unable to right themselves.

I have observed this countless times in a number of beetle groups. In fact,
while growing up I lived near Milwaukee, Wisconsin, in the US. We had a fairly
large population of Carabus nemoralis, which is a ground beetle that was
introduced from Europe into the US. I would frequently find beetles on the
sidewalks on their backs. No matter how many times they were righted, they
would invariably end up on their backs again, soon to die. I also observed
beetles stagger out of the vegetation bordering the sidewalk, only to fall
onto their backs. If these beetles were placed on their feet, even in the
vegetation, they would stagger about and would fall onto their backs again
when they encountered the sidewalk.

So, I suspect that the poor design is really a combination of dying beetles
coupled with a smooth, hard surface – one that is not normally found in
nature. Considering that roughly one out of every five living creatures is a
beetle, and that they occupy virtually every niche and habitat known, I would
suggest that beetles are, in fact, very well designed animals.