Fatal attraction: how street lights prevent moths from pollinating

Callum Macgregor, University of Hull/Newcastle University

For centuries, we have observed that artificial sources of light hold a strange fascination for moths. Despite decades of research, we still don’t know the cause of this attraction. Some theories put it down to the way moths navigate; others think it’s a mechanism to help them to escape from perceived danger. But the truth is, little evidence exists to support either of these ideas.

Whatever the cause is, research has shown that this deadly attraction may have even more sinister consequences than we first thought. In an open access paper in Global Change Biology, my colleagues and I describe the first evidence which shows that the effects of artificial light on moths may have serious implications for the wider ecosystem.

There has been plenty written about the danger posed by declining bee and butterfly populations, on the basis that some plants rely on these insects to carry pollen and fertilise flowers, in order to reproduce. But many people aren’t aware that moths also perform this task: our study of field sites across Oxfordshire found that one in four moths were carrying pollen, from at least 28 different plant species.

Danger zone.
from http://www.shutterstock.com

And like their cousins the butterflies, moths are in trouble: according to Butterfly Conservation’s Richard Fox: “the total abundance of moths in Britain has decreased by over a quarter since the 1960s”. Research indicates that artificial light, such as street lamps, has contributed to this decline by affecting moths’ development, reproduction and ability to escape predators.

Now, our data suggests that street lights are also directly thwarting night-time pollination, by attracting moths upwards, away from the fields and hedgerows. We found that the abundance of moths at ground level was halved in lit areas, while flight activity at the height of the street light was nearly doubled. The diversity of species was also reduced at ground level, with 25% fewer moth species in lit areas, compared to places without street lighting.

This change is likely to disrupt nighttime pollination by moths, and indeed we found some evidence that moths may carry less pollen, from fewer plant species, in lighted streets. This could mean that the impacts of street lights go beyond posing a health risk to moths. Plants that rely on moths for pollination would also suffer if their reproduction is impeded – and this might, in turn, affect organisms that eat those plants or drink their nectar.

In a best-case scenario, some of these so-called cascading effects might be mitigated where flowers can rely on other insects such as bees for pollination. But there are further factors driving declines in pollinator populations, such as climate change, pesticides and habitat loss. Now, our research suggests that artificial light can be added to the list.

Unnatural selection

So how can we protect these beautiful, under-appreciated insects and the important role they play in our environment?

The Spindle Ermine moth knows what’s good for it.
gailhampshire/flickr, CC BY

Another recent paper published by researchers in Switzerland suggests that moths may be evolving to be less strongly attracted to lights. Under controlled experimental conditions in a flight cage, they found that Spindle Ermine moths from urban populations were less likely to be captured in light-baited moth traps than their rural counterparts.

These findings suggest that moths which can resist the temptation of lights put themselves at a significant advantage over their peers. Over time this has led city-dwelling moth populations to become less attracted to lights, through natural selection. But this is all relative: urban moths are still far from immune to the deadly allure of urban street lights.

We can’t simply switch street lighting off: although the evidence for its actual benefits is questionable, it certainly contributes to many people’s feeling of safety and security when outside after dark and proposals to turn lights off are often unpopular.

But if we don’t wish to wait for the slow crawl of evolution, it may be that recent advances in street lighting technology can help to mitigate the impacts of artificial light. For example, developments born out of a desire for energy efficiency could also minimise the impact of street lighting on moths. Measures such as switching on street lights for part of the night, dimming them or introducing motion-activated lighting would reduce moths’ exposure to street lights. Similarly, the flexibility of LED lights might allow for the creation of street lights that are less attractive to moths, which respond most strongly to short-wavelength blue light.

Nevertheless, artificial light at night continues to increase as we seek to drive darkness from the streets. Our research is another warning that this may have far-reaching consequences for the organisms around us.

The Conversation

Callum Macgregor, PhD Candidate, University of Hull

This article was originally published on The Conversation. Read the original article.

Street lights alter moth activity

This post was originally written for the Butterfly Conservation blog and focuses on the contribution this marvellous charity makes to our research on moths, pollination and light pollution.

Newcastle University PhD student Callum Macgregor explains how a new study has revealed that street lights alter the activity of moths.

The findings of the study, an Open Access paper published today in the scientific journal Global Change Biology, could have potentially serious implications for wildflower species. 

The study forms part of a three-and-a-half  year research collaboration between Butterfly Conservation, the Centre for Ecology and Hydrology (CEH) and the Universities of Newcastle and Hull.

Small Elephant Hawk-moth with Greater Butterfly Orchid pollinia (John Bebbington)3
Small Elephant Hawk-moth carrying Greater Butterfly Orchid pollen. (c) John Bebbington

It is widely accepted that butterflies are among the most important groups of pollinators but the majority of our species of Lepidoptera are moths. As a PhD student co-supervised by Butterfly Conservation staff, my supervisors and I have set out to establish the importance of moths to pollination in the UK and abroad. In a paper published last year (which you can read here), we reviewed evidence from around the globe that moths are important pollinators of a diverse range of plant species, including some evidence of a role in the UK.

Butterfly Conservation’s 2013 report The State of Britain’s Larger Moths showed that our native moths are in trouble, with two-thirds of widespread and common macro-moth species in decline over the last 40 years.

Among the likely causes of this decline is the continuing increase in the use of artificial light at night to illuminate our streets, parks and gardens. Moths are known to be attracted to sources of artificial light and there is a growing base of evidence that this could affect their growth, reproduction and ability to escape predators. We were interested in whether the effects of artificial lights on moths could alter their role as pollinators.

Our research revealed that moth activity in street-lit areas shifts from vegetation level to lamp-post height, with lights attracting moths away from the fields and hedgerows. Moth abundance at ground level was halved in lit areas but flight activity at the height of the street light was nearly doubled. Around a quarter of moths were carrying pollen (from at least 28 plant species), supporting the idea that moths make an important contribution to pollination in the UK. However, we found some evidence that moths may carry less pollen, and from fewer species, in street-lit areas.

Dr Darren Evans of Newcastle University, one of my lead PhD supervisors, compares these findings to worries about more well-known pollinators, bees and butterflies. he said: “There is a great deal of concern at the moment about our falling pollinator populations and the knock-on effect on plant pollination. Our research suggests that it’s a process that is being damaged on two fronts – night and day”.

The project is funded under the NERC Industrial CASE studentship scheme, which aims to place PhD students into “mutually beneficial research collaboration between academic and non-academic partner organisations”. Acting as the CASE partner on the project, Butterfly Conservation staff including Head of Recording Richard Fox, Zoe Randle, Les Hill, Mark Parsons, and Director of Conservation Nigel Bourn have all been able to advise and shape this research.

Richard in particular is one of my PhD supervisors and a co-author on the paper. He said: “Moths are an important part of the UK’s biodiversity, as pollinators of wild flowers and as food for many birds and predators. The role of artificial light in causing moth declines remains unclear, but this new research indicates effects not just on moths but on the whole ecosystem”.

We hope that our findings can help to conserve this beautiful and charismatic group of insects and the flowers that depend upon them. Dealing with an issue such as street lighting can be complex:

Dr Michael Pocock of CEH, my other lead supervisor, said: “Street lighting at night is important for road safety and people’s security but our research is just the latest piece of evidence showing the unintended negative effects of street lighting on wildlife”. We are now investigating a number of recent advances in technology, such as the rise of LED street lighting, to see whether they may offer opportunities to reduce these negative effects.

Follow me on Twitter @Macgregor_Cal 

Coming out of the closet: why I will always love moths

Ask people to describe what they associate with butterflies, and you will probably get an image of a sunny summer’s day, with a beautiful peacock drifting gently on the cooling breeze.

Ask the same question but for moths, and you are more likely to be told about holes in a favourite woollen jumper, or something small and brown beating itself to death against a bathroom light fitting. We don’t view moths with the same affection as their day-flying cousins, and the irrational fear of moths is even common enough to have a name: mottephobia.

To my mind, this is unfair. Let’s start with the clothes-eating accusation. According to the charity Butterfly Conservation (which also protects moths), there are around 2,500 species of moths found in the UK; of these, only two will attack clothes. They prefer dirty items in undisturbed places: that means that if your jumper has been attacked, you probably weren’t wearing it often enough anyway.

In fact, there are also moth species that are crop pests, such as the diamondback moth, and some which produce irritant hairs as caterpillars – the non-native oak processionary moth currently infesting London is one such example. But again, these examples are very much in the minority among the total diversity of moths, and there are very many more reasons to love moths than to hate them.

Birch or buff-tip?
Callum Macgregor, Author provided

Many moths are just as beautiful as butterflies; some even look like butterflies! A particular favourite of mine is the brimstone moth: exactly like the brimstone butterfly, it is so-called for its vivid sulphur-yellow colour. Some are superbly camouflaged, like the buff-tip – easily mistaken for a broken twig of silver birch. And some have attractive names to match their appearance, such as the fabulous Merveille du Jour (“marvel of the day”), pictured at the top of this article.

Moths are vital pollinators

But beyond their beauty, moths also perform vital roles in the natural communities to which they belong. Along with colleagues, I recently examined the scientific literature to establish how important moths are to flowering plants as providers of pollination services. Most moth species that feed as adults do so by drinking nectar, and in doing so accidentally carry pollen between flowers.

We found examples of moths serving as important pollinators across many important habitats and in every continent except Antarctica. Several studies suggested that moths were the second most important pollinators in the area surveyed, behind only bees. In the UK, moths might be pollinating wildflowers near you including honeysuckle, bramble, white campion, wild carrot, thistle and ragwort. In North America, moths pollinate many types of cactus, and milkweed (beloved of caterpillars of the monarch butterfly). Globally, they are also well-known pollinators of many orchid and lily species.

If you’re a bird or a bat, a moth makes for a tasty treat. Researchers from the University of Bristol have examined the diet of two species of long-eared bat in England, revealing that their main food source was large-bodied moths from the Noctuidae (or owlet moth) family. Whereas bats (and the eerie nightjar) eat adult moths, moth caterpillars provide a vital food source in the spring for young birds including blue tits, which can munch their way through 35 billion caterpillars in the UK every year.

The moth-munching blue tit.
OliBac, CC BY

Especially important in this regard are those moth species that are active as adults through the winter, including the aptly named winter moth; these species reach the caterpillar stage of their life cycle at exactly the right time of year for busy blue tit parents to exploit.

And did you know that one species of moth has been domesticated into a valuable commercial livestock species, at the centre of a multi-billion dollar global industry? When spinning a cocoon in which to undergo the transformation to an adult moth, the caterpillars of the domesticated silkmoth Bombyx mori produce lustrous threads several hundred metres in length. These threads, once unravelled, are spun into the fine textile silk.

And if none of this has convinced you, know this: butterflies are actually just a minor subset of moths!

The Conversation

Callum Macgregor, PhD student in Ecology, University of Hull

This article was originally published on The Conversation. Read the original article.