Unless you’ve digitally cleansed your life recently, you’ll probably be aware that moth memes have taken over the internet – so much so that there is now, inevitably, a Reddit page dedicated to this unique sub-group of social media fodder.
The focus of this frenzy of meme-making has been moths’ famed love of artificial light. But here at Mastering Entomology, we’ve decided to delve a little deeper.
First and foremost, though, it’s worth pointing out that there are plenty of moths that fly during the day – so aren’t the types to be suckered into the seductive glow of a lamp. A study by Florida Museum of Natural History suggested that 15-25% of all Lepidoptera are day-flyers, while Butterfly Conservation has helpfully produced an overview of the UK’s non-nocturnal moths.
But of the nocturnal species, is there really a deep craving driving moth orientation towards our light sources? The fun-killing simple answer is probably no. The expert consensus seems to be that it’s all a misunderstanding; that they’re actually looking to orient themselves by the moon, and they’re simply drawn to alternatives because they’re brighter. As they move closer, their ability to triangulate is thrown off kilter, resulting in them returning to the light repeatedly.
But given the distraction, as opposed to attraction, our light sources bring, are all moths equally likely to zone in on the bright lights, and are all electric lighting types equally likely to bring lepidopterans into their glow? That’s another no and no.
The tendency to head for the light could be greater for moths from areas with little light pollution. Altermatt and Ebert (2016) found that in the case of the small ermine moth (Yponomeuta cagnagella), ‘city moths’ from populations that had experienced high amounts of artificial light were less likely to fly to light under lab conditions than those from ‘dark sky’ populations. It has been suggested by several studies that natural selection should favour those less drawn to artificial light – pretty logical stuff – and this research provides some evidence that such selection may indeed be happening.
Altermatt and Ebert have serious form when it comes to advancing knowledge on moths and light. In their 2009 study with Adrian Baumeyer, male Yponomeuta cagnagella and Ligdia adustata were seen to be 1.6 times more likely to make a beeline for an artificial light source than females. A good argument to settle the ‘smarter sex’ debate, perhaps.
A PhD study in Exeter has recently shed further light (pardon the pun) on the type of illumination most attractive to larger moths, finding that short wave lighting attracts both greater numbers of species and individuals than long wave.
The interplay of moths and light is, alas, not all online laughs and levity. There is growing evidence that artificial light may be having deeper effects on moth numbers than simply the deletion of those flying at speed towards the lamp. While the fact they are drawn to light is firmly established, there is evidence that it could be reducing moths’ attraction to each other.
A 2015 study in the Netherlands by van Geffen et al looked at the mating habits of Operophtera brumata, a member of the Geometridae family, when tree trunks were lit with different-coloured LED lighting. What the first phase of the research discovered was two-fold, and fascinating: a significant reduction in females on the illuminated trunks, again suggesting a sex bias in light attraction, and an inhibition of mating when they were under the lights. A side note, though: perhaps appropriately for this sexy moth discussion, more females caught on trunks lit with red light had mated than those with green or white light.
Mating is not the only matter that will pique concern amongst conservationists. Other research has found links between feeding and artificial light (they appeared to do less when subjected to it) and caterpillar development (they reached lower mass under white light and pupated earlier under green and white).
There is clearly multi-faceted interplay between moths and light, and a sense that we’re only beginning to understand the mechanics and effects of it. The ability of species to coexist with increasingly dense human habitation is a hot topic, so knowledge in this area is only set to grow in the coming years. Far from every aspect of this issue has been covered in this blog, but in the interests of brevity, it might be best to wrap up (although most of those readers who came for the memes have probably gone already).
Final note: this week and next we’re doing the taught elements of Biology and Taxonomy of Insects, the second module of the Entomology Masters here at Harper. Next Wednesday we’ll be looking at Lepidoptera, increasing our knowledge of these complex yet internet content-friendly insects.