Category: Science

The names of moths are marvellous. You’ve got your Death’s Head Hawk-moth and your Flame Shoulder, then there’s the Black Rustic and the Rustic Shoulder Knot and not forgetting Angle Shades. There’s even a moth known as The Uncertain. Then, there are the carpet moths. These aren’t carpet-eating moths, they’re species so-named because of their whimsical resemblance to patterned carpets.

Carpets, you say? How exciting…

Well, back in the day when pioneering naturalists were first recording all these different species carpets were exciting…well, if not exciting, certainly a luxury. Nobody really had carpets back then, the rich and landed gentry aside, and even then a carpet was a special thing, an underfoot treat not to be down-trodden nor trampled underfoot.

The Burnished Brass and the Feathered Gothic might have a kind of steampunk glamour to our ears, but in 1775 when Denis & Schiffermüller, identified, pinned, and named the Least Carpet, Idaea rusticata, the name was not an insult it was a compliment. Although, that said, this particular species doesn’t look like much of a luxury carpet being as it is, camouflaged to look like a bird dropping.

The Least Carpet is found across Europe, the Middle East and North Africa. In the UK it was initially found only in London and then the south-eastern counties it extended its range and abundance between 1968 and 2007, although records as far north as Cheshire dating back to 1999 may well be of migrants/vagrants.

Oh, and just to reiterate…the Carpet moths do not eat carpets. In fact, no moths eat carpets and only the larvae of a tiny handful of species eat textiles, such as wool. Many larvae eat plants of course, some carrion, but while we imagine the bees are the most important of our pollinators, moths are a major factor in doing that job too. #MothsMatter And, of course, they and their larvae are an important food source for birds and mammals, including bats.

Moths are drawn to flames, to bright lights, and as any good moth-er knows, ultraviolet. But why? That question has no answer…yet…although there is plenty of #DeceivedWisdom.

The first and perhaps most well-known explanation as to why moths are drawn to light is that they normally use the moon to navigate and an artificial light confuses their biological sat nav. This is very unlikely. Most moths don’t migrate and in general, don’t really need to navigate they just need to flutter around their locale to find food and a mate.

But, some moth-ers might say, there is always less of a haul in the UV scientific trap on nights when there is a full moon. The obvious explanation for that is that moths are simply less active because the night itself is brighter and they would be more exposed to predators, as they might be during the day. Although, bats are one of their biggest predators and, of course, they don’t rely on vision to catch moths, rather echo location.

Lots of species aren’t drawn to light at all, they prefer odour and specifically the pheromone odour of the female, at least that’s the case of the day-flying males of the Emperor species, discussed here previously. 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. But, while those pheromones can be made to glow under certain conditions, generally in a laboratory, they don’t glow at the same wavelengths as ultraviolet. More to the point, females are drawn to light too, so it’s probably not about moth sexual attraction.

My own pet theory, is that there’s some kind of confusion in the moth brain when they see a light. Perhaps there is some kind of “cross talk” between their senses (the same kind that we know of in people with synaesthesia who can smell colours or see music). Could those moths that are drawn to light be anticipating something else, maybe the light “smells” like food or sex attractants.

Maybe it’s a more blunt effect. The light source saturates their senses and stimulates the reward neurones in their brains as might an orgasm in higher animals or, indeed, opium derivatives, and in doing so in such an intense way that they cannot help but be drawn to that flame and to circle it.

Gunnar Brehm of the University of Jena, Germany, told me that, unfortunately, there is no answer to the moth-to-a-flame problem. “It would be great to have one,” he said. “I agree that the moon theory is not likely to apply and some sort of confusion happens.” So, perhaps my theory is close to what’s actually going on…

Brehm adds that “Short wavelengths at night have simply not been there before humankind invented artificial lights.” He and his research team are currently working on the problem. “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 told me. “However, when I replace UV by red the next night, the majority of moths is then attracted to blue.”

This suggests that short wavelengths (higher frequency, greater electromagnetic energy) are always the most attractive ones to moths that are attracted to light. Brehm adds that, “When there are no short wavelengths, a yellow light can also attract insects. That explains why moths can still be attracted by candlelight.”

Of course, the shorter the wavelength of light, the higher its energy in the electromagnetic sense. I’m talking light energy here, not the electrical wattage of the bulb. My hypothesis about why moths, and other insects, are attracted to light would fit with this, more energy would be more stimulating. Males are more frequently attracted to light than females, so, again this suggests the male moth psyche perhaps seeks out the stimulation or is more readily bedazzled by it.

In the absence of UV, much lower energy yellow light would have to suffice and would have done for millions of years before humanity came along with its actinic, fluorescent tubes, mercury vapour lamps, and UV LEDs.

UPDATE: 30 Jan 24 – New work from Sam Fabian, an entomologist at Imperial College London suggests that moths try to put their backs to any light source and this is why they end up spiralling around a lamp. That, doesn’t seem to explain what initially draws them to a flame or lamp, however.

Fellow moth-ers might be interested in Brehm’s work on assessing UV LEDs for attracting moths here and here. He and his colleagues 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 with the source at a standard output energy (unrelated to the radiation frequency/energy).

“We are working with modified types of the described lamp (first reference above), and it was possible to standardize the wattage of the lamps; so the emission is very similar but the wavelength is different,” Brehm told me. “We number each specimen, determine the sex and count each day what is caught and not caught.”

Brehm’s team has found significant differences between species: in some, males and females are attracted in similar quantities, in others far more males are attracted, but the attraction of short wavelengths appears to be rather universal,” he adds. The research will be written up for scientific peer review and publication later this year.

Despite a very wet night, there were 68 moths of sixteen species drawn to the actinic light trap overnight, including just one that was new to me, the Small Elephant Hawk-moth, Deilephila Porcellus. Unlike most of the other Hawk-moths, this one seems quite small, although bulkier than the vast majority of moths. The Small EHM has the same pink and olive colours as its cousin the much larger Elephant Hawk-moth. The Small EHM has a wingspan of about 40-45mm while the ever-so-slightly duller, but nevertheless gaudy, EHM is 45-60mm.

Neither moth is named for its colouration nor for any resemblance to elephants pink or otherwise, the name refers to the larva, the caterpillar, which is dully and greyish brown and somewhat wrinkled and looks a bit like an elephants trunk. Two large “eyes” at one end might be interpreted as the trunk’s nostrils whimsically.

Usually, you visit an RSPB bird reserve to see the birds. There’s often other wildlife, plants, scenery too, but the usual focus is the birds. Months ago, we booked our place on one of the infrequent but regular site open days at the otherwise “closed to the public” RSPB Hope Farm in Cambridgeshire. Having partied with our choir last night, we almost missed our day out on the Farm.

There were lots of families enjoying the sunny spells and the warmth, making wormeries, netting insects, partaking of the icecreams and Scout barbecue. So, instead of attempting to do any bird watching, we joined a guided tour of the wildflower meadows up the hill to see butterflies and saw quite a few nice species: Common Blue, Small White, Large White, Painted Lady, Small Tortoiseshell, Meadow Brown, Gatekeeper, and maybe one or two others. There were a few micro moths flitting about too.

Mrs Sciencebase had actually spotted something orange and unusual at the beginning of the walk after we’d watched Mullein moth caterpillars feeding on a mullein plant. Mullein moth adult is in my Mothematics photo gallery, pictured below:

The orange moth was definitely a day-flying moth, nobody, including the guide knew its identity. I took photos and after the tour, we headed to the identification station where they had books and neither the guide nor myself could find it in the moth book. Mrs Sciencebase tried the butterfly book, which had a day-flying moth section and almost immediately ID’ed it as the Burnet Companion moth, Euclidia glyphica. Nice.

Trip to RSPB Hope Farm also fed into our #PondLife as we bought some wildflower plants to add to the area behind the pond to help “wild” it a little more: Wild basil, Foxgloves, Red Campion, St John’s Wort etc

I had a discussion recently with a former moth-er who disposed of her trap after having an ethical pang of conscience about all the moths she had been disturbing over the years. She suggested that there are hundreds of thousands of people trapping all over the country and that we’re interfering with reproduction cycles by doing so. I felt her opinion was at best misguided.

My immediate thought was that that number was way off. I know two other people in this village of 4000 or so who trap regularly, as do I, but this is quite a sciencey village, close to Cambridge, so could be exceptional. There’d have to be 3-4 people in every of the 44000 villages and towns across the UK for there to be hundreds of thousands of people trapping. This from a straw poll I conducted among moth-ers online is very unlikely. If anything there are a few hundred across the British Isles mothing regularly, maybe at most 1000. Even if we assumed 1 per 1000 households, there are just 28 million households, that would still only be 28000, but I reckon the hobby is done by far fewer people.

Gary G: I’m not a moth trapper, I joined to learn more about moths. From my experience collecting ladybirds using sweep nets and beating trays I often find they mate in my specimen tubes before I release them. I wonder if this happens in moth traps?

Alan S: Yes it does. Sounds like [mating in moths traps] might be a beneficial side effect then. Add to that the huge benefits gained for ecology from recording the moth distribution and population trends and I’d say you’re on to a winner.

Jerry S: Also, more male species seem to be attracted to light.

Alan S: In the grand scheme of things it doesn’t make much difference unless people are constantly trapping the honeypot sites for scarce species and even then as long as it’s catch and release it should be OK. We survey lots of sites and these don’t get done as regularly as we’d like. The sites are huge and we only cover a tiny fraction each time we survey so impact is negligible.

Shaun P: If trappers are doing the right thing and sending in records, it should be easy to find out the number. I’m in Cornwall and I suspect the number of regulars is quite low judging by records and talking to others.

Sean O: Cars are a bigger problem…a drive in the countryside at night, moths continually in the headlights with several hitting, then multiply that by the number of cars on the roads around the country…that’s a lot of moths in a year!

Giles K-S: My experience (in rural Herefordshire) is that I actually see very few moths in the headlights – so few that you can almost count them individually. I think it’s just a symptom of the wider decline in insect numbers.

Mark G: I hardly see any. I remember the moth snowstorms of old in the 1960s.

Sciencebase: Yes, been discussing this for a while, 15-20 years ago, driving anywhere meant cleaning the windscreen regularly, not so these days.

Giles K-S: Moth traps only attract moths passing within a very short distance of the trap – in the range of 3 to 10 metres. Of much greater concern is the large number of other artificial light sources disrupting the activity of moths, bats and other nocturnal species.

Mark S: There are certainly [fewer] than 150 trappers in VC55 Leics & Rutland, and I’m sure there are many VCs with many fewer. Responsible catch & release, and recording does far more good than damage.

Leonard C: Static traps run all the time all around the country and provide valuable data. The only way we can help decline is to actually record numbers and then act upon such data by increasing habitat and foodplants.

Summer de G: [Moth-trapping] probably has no more impact than leaving outside lights on all night or garden lights.

Ben S: Moths are at more danger from birds, the bat roost at the bottom of my garden, artificial lights at night, and our clearing land, driving our cars etc.

Derek C: [Simply] mowing the lawn probably [kills] quite a few!

Kiera C: I think moth people are likely to be far less of a problem than the broadcast application of pesticides by industrial agriculture, the destruction of habitat, and the effects of climate change. If trapping and freeing moths just gets people to think about those bigger issues, to join environmental groups, to change their patterns of consumption, and to see the beauty in nature so that they want to look after it and protect it, then that possibly outweighs harms.

Lee T-W: I find that numbers in my garden increase slightly year on year (for common species). I wonder if attracting them brings them together to create greater breeding opportunities, also trappers are likely to manage their mini-habitat more beneficially?

Pete M: As long as people are sensible with holding off if you’re attracting predators, do all you can to prevent casualties, don’t trap every single night, and always send records in so your data has some use, I can’t see any real ethical issues.

It’s always a delight to spot a big lep in the scientific trap when you approach it each morning. This morning’s treat was a Privet Hawk-moth (Sphinx ligustri), but once I’d lifted the lid I realised there were two. This is a big moth (55 mm from the nose to wing-tip, with startling pink and black markings on its body and hindwings, which are revealed when it opens its wings.

This is the largest resident moth species in the British Isles. It flies June to July in a single breeding season. I had previously seen and phone-photographed a pair roosting on a concrete bollard in the village (14 Jun 2019, 21h20, Wilkin Walk, Cottenham, to be precise). But, not seen any since.

In repose, the Privet Hawk-moth is, like many other species, well camouflaged against natural backgrounds, such as leaves and bark. Its startling colours when it opens its wings are presumably an anti-predator adaptation like those of many other species, but not latching on to the “eyes or face” type of the Eyed Hawk-moth or the Emperor Moth. Black and pink stripes are more likely to be perceived as venomous or otherwise poisoning, bad-tasting, or stinging.

A Peppered Moth, Biston betularia, was drawn to my scientific moth trap last night. This species is probably the most important moth, scientifically speaking. It’s something of a Victorian scientific hero, in fact, and a speckly example of how evolution doesn’t always need millions of years to happen, but can take place within a decade or so if not faster.

During the sooty days of the Mancunian branch of Britain’s Industrial Revolution, this creamy white moth with black peppery speckles evolved to an almost black form (Biston betularia betularia morpha carbonaria). Originally, the light form had been well camouflaged on lichen, which meant it was hard for birds to see and so safe from becoming avian lunch. But a lot of the lichen was killed off by the smoke and smog of the industrial revolution and coated with soot. Those mainly white Peppered Moths were no longer well camouflaged and were easy pickings for birds.

However, a mutation arose in this species that for all intents and purposes gave rise to a melanic, dark, form of the moth. No more bright white but a sooty black moth that was now camouflaged on the dark surfaces of the industrial era. Now, the dark moths that evaded detection by birds could live to breed and pass on their genes for this melanism. It seems that the mutation arose around 1819 as the carbonaria form was not noted by naturalists before this date.

The rapid change from a bright to a dark, melanic form, industrial melanism as it is now known, provided evidence of survival of the fittest, natural selection, and evolution in action. By the end of the century, 95 per cent of the Peppered Moths in Great Britain were carbonaria.

The melanic form began to decline in Britain after the Clean Air Act of 1956 when smokeless fuels came to the fore and uncapped pollution was no longer acceptable. I am yet to see the melanic form, hence the lack of photos, but it certainly still exists in the wild. This reversal of the adaptation lends additional support to the evidence for the original industrial evolution.

There was some concern in the 1990s that the original research proved nothing as it didn’t take into account the moth’s natural resting places and that moth migration might skew the actual results and may have led to some of the effect. However, interesting research by the late Michael Majerus discussed and followed-up here in the journal Biology Letters provides strong evidence that reinvigorates the original hypothesis of industrial melanism in the context of predation by birds.

The authors talk of how “caveats about the predation experiments discussed in Majerus’s book, critiques by other biologists, as well as points made particularly forcefully in a review of the Majerus book, were soon exploited by non-scientists to promote an anti-evolution agenda and to denigrate the predation explanation”. They add that “both the public in general and even evolutionary biologists began to doubt the bird predation story.”

Their paper also debunks the creationist ideas that arose when doubt was first cast on the idea of this rapid evolution of an animal as its surroundings changed through industrialisation and into the post-industrial world of the North of England. Moreover, industrial melanism is seen in other types of moth and provides parallel evidence for the changes observed in the industrial evolution of the Peppered Moth.

UPDATE: 25 Jun 2019 – Another Poplar turned up overnight along with two Privets, an Eyed, six Elephants, and a Small Elephant! And 150 other miscellaneous specimens.

My first taste of mothing proper was in a friend’s garden, where I turned up at about 8am the night after he’d “lit up” his 40W actinic, homemade, collapsable Robinson trap. I mentioned it on the blog at the time, you may recall – The Nouveau Mottephile. Regular readers will have noticed I’ve blogged about moths quite a lot since that fateful July morning. Anyway, on that morning I was startled by to be introduced to the diversity of the Lepidoptera, there were a few dozen moths in my friend’s trap, almost all of which I had never seen before. I only had a phone with me so, the photos I got were of poor quality. One of the most startling and beautiful moths in the trap is the subject of this post, the Poplar Hawk-moth (Laothoe populi).

The description on the UK Moths website about the Poplar Hawk-moth reads as follows:

“Probably the commonest of our hawk-moths, it has a strange attitude when at rest, with the hindwings held forward of the forewings, and the abdomen curved upwards at the rear. If disturbed it can flash the hindwings, which have a contrasting rufous patch, normally hidden.”

This specimen was in the trap this morning, the same trap, which I bought from my friend in the autumn of last year, having become hooked on mothing. It’s the first time I’ve seen this species since July 2018. I photographed it but obviously didn’t irritate it at all as it never flashed its underwings.

Other Hawk-moths that have featured on the blog:

Lime Hawk-moth, Mimas tiliae

Elephant Hawk-moth, Deilephila elpenor

Eyed Hawk-moth, Privet Hawk-moth, Small Elephant, Pine Hawk-moth, and Hummingbird Hawk-moth are in my Mothematics gallery.

As of 10 May 2022 yet to see or photograph: Death’s Head, White-lined, Convolvulus, Oleander, Willowherb, Spurge, Bedstraw, Striped, Silver-striped, Broad-bordered Bee, and Narrow-bordered Bee Hawk-moth.