On Saturday night I stood in the field just outside our Dordogne holiday gite and gazed skywards. I was looking for Perseids, the late July and early August meteor shower, a product of the Earth sweeping through the ghostly interplanetary remains of the Swift-Tuttle comet, which last passed through this neck of the solar system in 1992. Despite a relatively clearish sky, I saw no shooting stars. I did, however, find a grass star — a glow-worm, Lampyris noctiluca.
Bioluminescence is one of nature’s many magical things, and never fails to enthral me. I cupped the beetle in my hands and rushed indoors to show the rest of the family the glow-in-the-dark fairy.
Holding this small beetle and watching its not insignificant greenish glow on my skin I was reminded, yet again, just how miraculous the natural world can seem, even to the initiated, the educated, the experienced scientist.
Elsewhere in the world, glow-worms (and their New World equivalents the fire-flies) are also sources of childish wonder and nowhere more so than in Jamaica, where I’m reliably informed the children call them winkies, because of their bright and regular flashing.
Jamaica is home to one of the largest and brightest of fire-flies, Pyrophorus noctilucus. It’s not in the usual group of glow-worm or fire-fly beetles (family Lampyridae) instead it is a member of the family Elateridae, or click beetles (named for the audible click they make as they suddenly jack-knife to escape the would-be predator), nevertheless, for many years it was claimed to be the largest fire-fly and to produce the brightest light of any insect.
These claims (later verified) had the unexpected consequence that Pyrophorus was particularly sought after, not by the world’s entomologists, but by its nutritionists.
My informant is Dr Joan Stephen, who in 1954 helped set up, in Jamaica, the Tropical Metabolism Research Unit with Professor John Waterlow of the London School of Hygiene and Tropical Medicine. This was a time when the chemical understanding of nutrition (or malnutrition in this case) and metabolism was being unravelled. A field station in an impoverished and under-nourished Commonwealth country was one of many ways to find out how poor living, poor diet and metabolic imbalance could be a leading cause of death, especially in children.
Coincidentally, During the 1930s and 40s biochemists had finally worked out the basis of photosynthesis, as light photons hitting the chlorophyll in green leaves, released electrons through a cascade of reactions that finally promoted adenosine diphosphate (ADP) to the energetically more available adenosine triphosphate (ATP). ATP exists through all living organisms as the molecular currency of energy, energy used in every metabolic reaction, and a keystone to understanding how metabolism, and in its turn, nutrition, works.
In today’s high-tech labs it’s easy to forget that, in the 1950s, assays relied on boiling up substances in test-tubes with various reagents, and often manually checking subtle colour changes against printed colour charts. This was OK for roughly measuring the carbohydrate content of a pain-au-chocolat, or how much alcohol is in a bottle of Guinness, but ATP and ADP are highly reactive molecules that occur in truly minute amounts. An assay to measure their activities required a much higher level of analysis. And it was available thanks to glow-worms.
The cold light given off by these beautiful beetles, without heat, without combustion, is the exact opposite of photosynthesis. During a special chemical conversion, that energy-storing molecule ATP gives up its electron to produce ADP and as the reverse cascade of chemical reactions continues it produces back that photon, to shine out into the night sky to try and attract a fire-fly mate.
In the test-tube, though, that small light output could be accurately measured using recently developed photometry devices which offered an electrical means of measuring, comparing, and giving a fixed numerical value to spectacularly minuscule chemical reactions. The light-producing chemicals of the fire-fly, luciferin and its enzyme converter luciferase, offered a unique and super-sensitive assay for the newly discovered ATP/ADP energy reaction.
And, so it happened, Jamaica was also home to that giant and brightly glowing click beetle, Pyrophorus. This beetle’s light-producing chemicals were now in great demand.
In a low-tech twist, though, these chemicals could not be synthesized, but needed to be harvested from adult beetles, laboriously collected in the Jamaican hillside forests. However, rather than the scientists doing the collecting themselves, Joan Stephen was in charge of marshalling the local children. They collected the winkies and she paid them with pennies, she, of course, being known as “the winky woman with the pennies”.
The glow-worms here in the Dordogne are smaller, humbler and more discreet than Jamaican winkies, but still lovely and mysterious to behold. The Dordogne is at the centre of European ‘cave-man’ art, and, for a moment, I was tempted to imagine some long since vanished hairy, brutish Cro-Magnon man, clothed in rough mammoth-skin cloak and aurochs-leather leggings, bending down on a similar limestone hillside 15,000 years ago, scooping up a glow-worm in his gnarled hands and grunting in soft wonderment at his astonishing find. Sadly, there appear to be no insect-related cave pictures hereabouts, glowing or otherwise.