First, let’s dispel a myth. Not all moths are brown and boring.
Some species are colourful and just as beautiful as their butterfly cousins. But, their numbers are falling – which will have a knock-on effect on the environment and humankind.
There have been significant changes to moth populations in the UK over the last 50 years. The Atlas of Britain and Ireland’s Larger Moths, based on 25.6 million moth records submitted over 275 years, presents the most recent information on species distribution (where they are found) and abundance (numbers of each species).
The study looked at patterns of change from 1970-2016 and showed that 31 per cent of the 390 species had declined in distribution, while 38 per cent of species increased. What’s more, 34 per cent showed a significant decrease in abundance, while 11 per cent showed a substantial increase.
Put simply, moths are decreasing in numbers more than they are increasing.
Similar trends have been seen elsewhere in Europe. In the Netherlands, 71 per cent of larger moth species decreased between 1980-2009. While, in Finland, analysis of long-term distribution records showed significant overall decreases in the distribution of larger moths in some species.
BUT WHAT DO THESE CHANGES TELL US?
Moths are highly sensitive to environmental change, both in terms of the climate and in changes to their habitat.
Climate change is a major factor. A warmer climate will benefit some species, but negatively impact others.
Many species should benefit from a warming climate in the UK, as they can expand northwards where it was previously not suitable for them. “This is being shown in a number of species, particularly recent colonists,” says Marc Botham, an entomological ecologist at the UK Centre for Ecology and Hydrology.
“But many are still declining, despite expanding their ranges northwards, suggesting that habitat loss is preventing them from benefiting from improved climatic conditions.”
Some species found in mainland Europe are exploiting the warmer weather by hopping across the channel and successfully colonising in the UK.
“As is the case with butterflies, some moths are adapted to live in the climate as it was and will not like it getting warmer,” warns Barry Prater, county moth recorder for Berwickshire, Scotland. “If temperatures rise, suitable cool areas, particularly those at a higher altitude, will diminish and this will probably lead to further declines.”
They have short life cycles so they are good indicators to environmental change.
Moths have been likened to the ‘canary in the coal mine’ as they play a vital role telling us about the health of our environment. Historically, canaries were used in coal mines to detect the presence of carbon monoxide.
“They have short life cycles so they are good indicators to environmental change,” says Zoë Randle, senior surveys officer at Butterfly Conservation. “If their numbers are going down, they are like the litmus paper telling us things aren’t right in the countryside. And we need to do something drastic.”
Climate change is altering the flight period of some moths. Some are flying earlier in the year and some are flying later now compared to the 1970s. Some species are also having more than one brood per year, compared with the 1970s, and the occurrence of second broods further north are becoming more apparent with the changing climate.
THE ROLE OF MOTHS IN OUR ECOSYSTEM
There are many other limiting factors for moths. Availability of habitat, agricultural intensification, increased pesticide use and monocultures of crops are also affecting their numbers. Dr Botham notes, “losses are greatest in those species that have very specific habitat requirements. Showing and telling us that the state of our countryside is declining.”
This is not a good sign – as moths play an incredibly important role in our ecosystem.
Despite bees hogging all the attention, moths are important pollinators of plants. Dr Randle calls them, “the bees of the nighttime,” adding, “they are the night shift if you like.” About 85 per cent of crops within the EU are insect-pollinated.
Honey bees only actually pollinate about five to 15 per cent, which leaves the other 85 to 95 per cent to be pollinated by bumblebees, solitary bees, moths and butterflies and all sorts of other insects.
This crop pollination is estimated to be worth hundreds of billions of pounds annually.
And as moth numbers go down, animals that feed on them will too. They are major components of the diets of many other animals, including birds, bats and other small mammals. The diets of numerous bird species, especially their young, is largely made up of moth caterpillars. Blue-tit chicks consume around 50 billion caterpillars a year in Britain and Ireland, for instance.
There is also increasing evidence that light pollution may be contributing to declines in European moth populations.
“We don’t understand why moths exhibit flight to light behaviour,” says Dr Randle. We do know, however, that light pollution is disrupting their behaviour. Artificial light is affecting their migration, mating and feeding habits.”
The most obvious effects of light pollution are the adults being attracted to light sources; street lights, car park lighting and security lights. “This can disrupt them from their usual behaviours,” says Douglas Boyes, an entomologist and PhD student from Oxfordshire.
“They spend the night flying around a lamp, rather than feeding and mating.” It also makes moths much more vulnerable to predation, especially from bats. “Some bats actively forage around lamps,” he says. “Moths that are attracted to these lights can fail to display their usual anti-predation behaviours so are ‘sitting ducks’.”
HOW YOU CAN HELP MOTHS
For millions of years, life on Earth has evolved without any sources of artificial light. Boyes stresses, “our wildlife, and indeed humans, need dark nights.”
Now you are no longer in the dark about moths, here’s how you can help their dwindling populations.
Have a wildlife-friendly garden, even if it’s only a small patch. Plant good nectar sources for moths to feed on; honeysuckle, primrose and tobacco plant. Grow a mixture of different caterpillar food plants to get them breeding in your garden. Trees and shrubs are always good – ash, brambles and oak.
Let your grass grow, plant more native plant species and don’t be too tidy when trimming.
Moth recording by organisations like Butterfly Conservation, Moths Count and iNaturalist will help improve our understanding of populations, so conservationists can act before it’s too late.