Science & Environment

UK moth numbers suffer crash, 40-year study shows

V-moth (Image: Roy Leverton/Butterfly Conservation)
Image caption Moths are considered to be important indicators of biodiversity health

Two-thirds of Britain's 337 species of common larger moths have experienced a substantial decline over the past four decades, a survey has shown.

The V-moth (Marcaria wauaria), once a common sight in gardens, recorded a 99% fall in numbers from 1968-2007.

Habitat loss and deteriorating land are thought to be behind the decline.

The findings appear in the State of Britain's Larger Moths 2013 report, produced by Butterfly Conservation and Rothamsted Research.

"Larger moth in Britain are showing substantial and significant decreases in their populations over this 40-year period," observed lead author Richard Fox.

"This not only includes a big decrease in the total abundance of moths, but also a large decline in a large number of individual species."

"Generally speaking, these are common and widespread moths that live in our gardens and farmed countryside, so we are not talking about rare, special species."

Overall, the four decades of data showed that the total abundance of larger moths declined by 28%.

Changing habits

The biggest loser, the V-moth, was once found in most English counties but now its presence is restricted to "very few areas", Mr Fox, surveys manager for Butterfly Conservation, added.

"It is also quite an interesting example because V-moth caterpillars feed on gooseberry and currant leaves and, although we do not know why the species has declined, we are drawn to speculate that the decline of the V-moth might be something to do with our gardening habits.

"It may be that far fewer people grow their own gooseberries and currants in their gardens. Alternatively or in conjunction with this, it may be that people - especially in their own gardens - may be using pesticides far more than in the past."

He said that there was no clear evidence for the decline, but studies were finding that habitat loss and, as a result, diminishing food sources, were major contributing factors.

"In the farmed landscape, for example, intensification has removed hedgerows, hedgerow trees, field margins where there would have been wild flowers growing.

"Although we do not have a baseline of data that goes back to the pre-intensification of farming in Britain, there are quite a lot of studies that have been done which have shown that on farms where they do still have hedgerows, trees and wide field margins then that does have benefits, in terms of the variety of moths that are seen as well as overall abundance," he told BBC News.

He added that studies had also identified changes to forestry management and urbanisation as drivers for the decline in moths.

Silver lining

While the findings revealed a widespread overall decline, about a third of species did record an increase in numbers.

Among them was the footman group of moths, Mr Fox explained.

"The thing that they all have in common is that their caterpillars feed on lichen and algae.

"Again there is a temptation to wonder whether the improvement in these moths numbers and distribution might be linked to increases in the amount of food available to them in the landscape.

"This could be linked to improvements in air quality because lichens were greatly reduced during the time of acid rain and air pollution. We also have an increasingly nitrogen-rich environment that might be beneficial for algae."

The report's authors said that more than 2,500 moth species have been recorded in England, Wales and Scotland, of which about 900 are described as larger moths (macro-moths) and 1,600 micro-moths.

They added that the overall decline pointed to a wider insect biodiversity crisis and mirrored declines of butterflies, bees and carabid beetles.

"The declines could have a knock-on effect for plant pollination and animals reliant on moths for food, such as garden and woodland birds, bats and small mammals," they said.

Mr Fox highlighted that entry level enviro-agricultural stewardship schemes, such as the one funded by the EU's Common Agricultural Policy, offered a potential solution to halt the decline.

"They are aimed at large numbers of farmers and landowners doing simple thing that will put back some of the semi-natural features that have been lost in intensively farmed landscapes," he explained.

"The has been some really good research done in the past few years by Oxford University, in conjunction with Butterfly Conservation, that showed simply having trees in hedgerows on farms in lowland England has a really beneficial effect on both the variety and abundance of large moths that occur there."

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