Jonny Rogers explores how LED streetlights are affecting moth populations in the UK.
Photo by Thom Milkovic
Whether by campfire, candle or chandelier, human ingenuity has brought light to the shadows, blurring the boundaries of day and night. According to research from 2016, more than 80% of the world’s population live under light-polluted skies; the amount of land with artificial lighting at night is increasing by 2.2% every year. More than a third of all people can no longer see the Milky Way from where they live.
Although a brighter world means that we can work longer and travel further, it also entails the tragic loss of insect populations. A recent study on moth caterpillars in 26 sites across southern England found that street lighting ‘strongly reduced’ their abundance: by 47% in hedgerows, and 33% in grass margins.
Light Pollution and Moths
The researchers chose to focus on moths for a number of reasons: first, they have been closely studied for a long time; second, they are important for terrestrial ecosystems, acting as both pollinators for plants and prey for other creatures; and third, a number of countries have seen a significant decrease in moth abundance and diversity over recent decades.
In Britain, 34% of the most common macro-moths have experienced a notable decline between 1970 and 2016, accounting for a 39% decrease in the total number of larger moths in the south of England, and 22% in the north. One study from 2019 found that over 40% of all insect species worldwide are threatened with extinction, while some are also likely to bloom.
Of course, moths are not the obvious poster child for wildlife conservation; many people would undoubtedly rather live in a world without them. However, changes to any insect population can have significant consequences for entire ecosystems, disrupting both plant pollination and animal food chains.
This study takes place as the roads of Britain undergo a significant transformation – the orange aura of sodium streetlamps is being supplanted by the white glow of light-emitting diodes (LED). Although this shift is thought to be more energy-efficient, it will likely alter the navigation and interaction of the nation’s wildlife. As the recent study has shown, the negative effects of artificial light were more pronounced under LED than sodium lamps.
As moths have evolved to lay eggs in darkness, artificial lighting most likely disrupts their reproduction process, explaining why fewer moth caterpillars were found near the streetlights. In addition, increased artificial lighting means that moths are easier to spot for bats and hedgehogs, causing a disbalance in species population and diversity.
The study also observed changes to individual organisms – the caterpillars found in artificially lit areas were typically heavier, perhaps because the light increased the early rate of development. This might have a serious impact on the fitness of the adult moths, thereby affecting the health and abundance of future generations.
The Wider Impact of Light Pollution
While one might expect that the negative effects of artificial lighting would increase in proportion to its intensity, the impact of light pollution is, in reality, more complex. Research from the University of Exeter, for example, found that low levels of lighting (i.e. areas surrounding towns) gave parasitoid wasps an advantage in hunting aphids, while brighter lighting (i.e. urban centres) rendered the same activity more difficult.
Of course, the harm caused by artificial light extends beyond the behaviour and reproduction of insects. As shown in the heart-breaking conclusion to David Attenborough’s Planet Earth II in 2016, baby turtles, which hatch on beaches and are naturally guided towards the water by moonlight, are attracted to the bright lights of coastal towns. Additionally, the glare of urban areas can disorientate migrating birds, resulting in fatal collisions with man-made structures.
It might not be surprising to learn that light pollution is also a hazard to human health. As our minds and bodies naturally change in accordance with the 24-hour day/night cycle – our circadian clock – frequent exposure to artificial light, both in the home and outside, can contribute to depression, insomnia, cardiovascular disease and a range of other medical disorders. As Paolo Sassone-Corsi, chairman of the Pharmacology Department at the University of California, explains:
“The circadian cycle controls from ten to fifteen percent of our genes [...] So the disruption of the circadian cycle can cause a lot of health problems.”
Concluding Thoughts
As with noise pollution, light is often underestimated as an environmental threat, largely because we often think and talk about pollution as a matter of physical substances accumulating in particular spaces. However, this study adds to the large body of evidence that artificial lighting has provided benefits for human navigation at the detriment of both our health and the ecosystems we live in.
Nevertheless, it is important to recognise that the ecological impact of light pollution should not be taken in isolation from other activities associated with urbanisation and population growth. As Douglas Boyes of the UK Centre for Ecology & Hydrology explains:
“The main factors [of insect population decline] are climate change, habitat loss, agricultural intensification, and chemical pollution (including pesticides, nitrogen deposition), but lighting we expect will certainly be important in some contexts.”
Unlike many other forms of pollution, however, artificial lighting is relatively easy to change: the impact of LED streetlights can be mitigated by reducing their intensity, employing motion sensors, adding shields to focus the light on the roads or changing their colour through filters.
Although it is uncertain how and whether these factors will ever come into force, they must be taken into consideration as the world shifts towards more energy-efficient infrastructure. A greener future will have to be a little darker.
Article on a similar topic: The Unspoken Impact of Noise Pollution
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