Friday 23 February 2018

The insect that stays alive by 'playing possum'

Paul Bettany and Russell Crowe in the film of Patrick O'Brian's 'Master and Commander'
Paul Bettany and Russell Crowe in the film of Patrick O'Brian's 'Master and Commander'

Joe Kennedy

'Arcades ambo' - two rascals of weevils crept from crumbs on the captain's table as the decanter was passed along following a dinner of "capital sea pie", no doubt.

In Patrick O'Brian's first novel of the series, Master and Commander, Capt Jack Aubrey asks his bosom colleague, the ship's Irish doctor and naturalist Stephen Maturin, which of them would he choose.

"I should choose the right-hand weevil; it has a perceptible advantage in both length and breadth," replied Stephen.

"There I have you," cried Jack. "Don't you know that in the navy you must always choose the lesser of two weevils? Oh ha, ha, ha, etc."

This little joke made it into the script of the only film made so far of O'Brian's 23 novels about the adventures of the indomitable pair.

I read all of the books years ago, as did a couple of well-known persons to whom I recommended them, but none had the good fortune to meet the author in person except my old Independent colleague Gerry Mulligan (now with the HSE), who stopped O'Brian on a Dublin footpath for a friendly chat. O'Brian was staying in Trinity working on his last book.

The presence of weevils in flour and baked goods such as ship's biscuit was once fairly commonplace. I had thought that these were of the genus curculio, found in nuts and acorns, but I learn that the flour weevil is not a true member of the tribe at all, but is really a 'red' or 'confused' beetle.

I will not go further into this as a weevil of great interest to gardeners and plants-men is a creature which is also a first-class actor and which can cause havoc. This vine weevil can, at the first sign of disturbance, pretend that it is dead. Such stress-induced immobility, when the weevils lie on their backs, is called thanatosis after an ancient Greek deity, Thanatus.

The best known animal exponents of this deception are American opossums, which have given rise to the expression "playing possum", lying coma-like to avoid undue attention.

The distinguished zoologist and botanist Dr Phil Gates, a north of England academic, has described how a weevil, "at the first touch of my fingers", fell to the ground and pretended to be dead.

Vine weevils are well equipped for this. They tuck their legs under their barrel-shaped bodies and roll onto their backs. Being flightless and ponderous walkers, they have no other options when threatened, Dr Gates points out.

They linger awhile. Their mottled brown hues make them hard to see on the soil.

The insect under Dr Gates' scrutiny waited a couple of minutes before it began its tentative return to life, waving its legs and rocking from side to side. Then it got on its feet and rambled off.

Gardeners hate these creatures. Their shiny, white larvae feed underground and can destroy total root systems, especially with potted plants whose wilting leaves are the first signs of trouble. By then, it is too late. Gardeners tear their hair and cry out!

The weevils are difficult to control for an extraordinary reason, in that it takes just one of them to reproduce its kind. The females are parthenogenetic, laying fertile eggs without any male input. The offspring are clones of the mother.

As Dr Gates succinctly puts it, here is an animal with assured genetic immortality that has perfected the art of staying alive by feigning death, "an achievement worthy of the gods of ancient myth".

Sunday Independent

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