Britain's Largest Moths in Decline

1 March 2021

A new report, ‘The State of Britain’s Larger Moths’ produced by a partnership of Rothamsted Research, wildlife charity Butterfly Conservation, and the UK Centre for Ecology & Hydrology, shows a worrying 33% decline in the populations of larger moths in Britain over the last 50 years.

The report, the last of which was released in 2013, draws on tens of millions of records gathered through the Rothamsted Insect Survey and National Moth Recording Scheme (NMRS).

Rothamsted data shows the total abundance of larger moths in Britain decreased by 33% over a 50-year period between 1968-2017.

In line with other recent Rothamsted Insect Survey studies, this decline was seen across Britain with a greater loss in the south (39% decrease) than in northern Britain (22% decrease).

Dan Blumgart, Quantitative Moth Ecologist at Rothamsted Insect Survey says: “Comparing this latest State of Britain's Larger Moths to the first edition in 2006, it is a disappointment that the overall decline has not improved.

“It is clear that a much bolder policy of habitat protection and restoration will be needed if British moths are to thrive.”

This third assessment of The State of Britain’s Larger Moths is dedicated to Dr Kelvin Conrad who passed away in 2018 at the age of 56. His work on moth population trends at Rothamsted Research was the key driver for the first such report in 2006, which he co-authored.

The Rothamsted Insect Survey provided data from 527 traps which collected 764 species of macro-moth, of which 427 species were numerous enough to produce species-specific trends.

In total, the Survey recorded almost 12 million moths during the study period.

Long-term abundance trends showed 41% (175 species) had decreased and only 10% (42 species) increased, with the remaining 49% (210 species) having trends that did not show statistically significant change.

Dr Colin Harrower, Spatial Data Analyst at the UK Centre for Ecology & Hydrology, says:

“Our analysis of the millions of records showed that, over the past 50 years, four times as many moth species decreased in abundance as increased. It is possible that our rarest species, for which we cannot easily produce reliable trends, are facing even greater threats to their populations.”

Dr Richard Fox, Associate Director of Recording and Monitoring at Butterfly Conservation and lead author of the report added that the decline is worrying because moths play a vital role in our ecosystems.

“They are pollinators of many plants, with some wildflowers, such as orchids, relying on visiting moths for reproduction. They also provide essential food for thousands of animal species, including bats and many familiar birds.

“We’re lucky enough to have almost 900 species of larger moths in Britain. Because moths are dwindling, we can be pretty sure that other wildlife are also in decline and that our wider environment is deteriorating.”

Research into possible causes for the decline of larger moths is underway. Likely causes include habitat loss, light and air pollution, and climate change.

Of 511 larger moth species for which long-term trends could be calculated from NMRS data, 32% (165 species) decreased in distribution and 37% (187 species) increased, while 31% (159 species) had non-significant trends. Therefore, more moth species increased in distribution than declined.

A multi-species distribution indicator increased in extent by 9% over a 47-year period (1970–2016) and the northern range margins of moths have, on average, shifted northwards by 5km per year (1995–-2016).

The report concludes that more sympathetic management - such as through agri-environment schemes - and expanding, restoring, connecting and creating habitats that support a rich array of wildlife is the key to reversing moth declines.

The full report can be seen downloaded here.