"Like a moth to a flame". It is something of a rather well-worn cliché alluding to the attraction of nocturnal Lepidoptera for lights and how, figuratively, that describes someone as being attracted to something that is destructive. Shakespeare, in The Merchant of Venice (1596) talks of how "the candle singd the moath."

For the lepidopterists of the 18th Century when the panoply of the natural world was beginning to open up to their investigations. Nets, illuminated linen sheets, and naked flames were the only way to capture the myriad moths that were gradually emerging from the darkness.

Today, scientists - both professional and "citizen" have a whole range of novel tools with which to entice and capture their targets of study. Nets, still, of course, but actinic lights and purpose-built traps. The bulbs often being simple fluorescent tubes with an ultraviolet component, what might be colloquially referred to as "black lights". They also have fragile and water -sensitive mercury vapor bulbs that are well known to attract vast numbers of photophilic creatures - moths, beetles, bugs, even frogs and some other vertebrates.

There are also a wide range of pheromone lures that can be used. These chemicals are identical to the heady brew released by the female of the species to attract the male. They are more commonly used to attract day-flying moths such as the brightly colored male Small emperor moth with its feathery antennae and its pareidolic wing "eyes". Indeed, the mostly monochromatic female of the species spends her days exuding volatile (6Z,11Z)-hexadeca-6,11-dien-1-yl acetate to attract the males across spring meadows.

For several decades, lepidopterists have drawn in the "leps" with lamps and pheromones. Back in the day, the fate of thousands of specimens was the killing jar and the pinboard. But, broadly speaking the modern approach is to trap humanely ever so briefly, examine, perhaps photograph, and then release back into the wild. To follow the pheromone trail or find a new flame once more.

Now, the most vexing question that everyone is now dancing around the flame to know the answer to is, of course, why are moths attracted to light at all. They are largely nocturnal creatures, although there are many day-flying species. Why would a naked flame or the glow of a fluorescent or mercury vapor bulb be of interest? The aims of these adult creatures are ultimately to mate and create the next generation. They may well feed in the meantime to keep their energy up, often pollinating plants as they go, although many moths have no mouthparts (the Small Emperor included). Unfortunately, vast numbers are also bat-fodder each night, but that is another story.

So, what use to them evolutionarily speaking would there be in making a heading for and circling around a light?

The first and perhaps most well-known explanation as to why moths are drawn to light is that for millions of years they have used the light of the moon at night to help them steer a steady course and navigate their way around the countryside. Artificial lights simply confuse their biological sat nav. Moth enthusiasts often offer as evidence the smaller "haul" they see in their traps at morning light when there has been a full moon in the sky. To my mind, the more obvious explanation is that on a bright night moths are simply less active so that they can avoid being exposed to a greater variety of nocturnal predators in the moonlight. More damningly, many species of moth are not drawn to light at all, so what do those species do for navigation? And, what do the photophilic moths do on nights when there is no Moon?

There was a theory in the 1970s that suggested male moths somehow confuse the light source with the luminescence of the female's sex pheromones. This sounds rather spurious and does not explain why female moths are attracted to light. More to the point though, pheromone molecules don't tend to glow at the same wavelengths as candle flames and incandescent lightbulbs.

It occurred to me that there may be something akin to synaesthesia occurring in the moths. Perhaps there is some kind of "cross-talk" between their senses. The bright light stimulates them, and the cross-talk makes them interpret the signal as an attractive odor, associated with food or sex. It might even be blunter. The light source saturates their senses and stimulates the reward neurons in their primitive brains. The feeling is so intense that they cannot help but be drawn to that flame.

So, what has any of this to do with materials science? Well, the development of new materials has led to the development of novel ultraviolet light-emitting diodes (LEDs) that researchers are using to investigate that moth to flame question. Gunnar Brehm of the University of Jena, Germany, has been intrigued by the question for many years.

"We are carrying out choice experiments with different wavelengths - four lamps in four corners of a hall. When moths are offered white, green, blue, and UV, the vast majority is attracted to UV," he says. "However, when I replace UV by red the next night, the majority of moths is then attracted to blue."

This suggests to him that short wavelengths are always the most attractive ones. "When there are no short wavelengths, a yellow light can also attract insects," he says. "That explains why moths can still be attracted by candlelight."

Brehm's team have pioneered lepidopteral science with UV LEDs. One advantage is that LEDs can be very precisely configured to give a particular range of wavelengths at a specific wattage. This means they can be used to test attraction at different wavelengths without the output power. The team has modified the LEDs to standardize the output wattage so that the emission is very similar but the wavelength is different. The attraction to short wavelengths appears universal.

Of course, the shorter the wavelength of light, the higher the energy of that light. His findings would thus fit my stimulation hypothesis. Higher energy presumably equates to greater stimulation. Lower energy yellow light sufficed for millions of years before humanity and its actinic, fluorescent tubes, mercury vapor lamps, and UV LEDs.

David Bradley