The new State of Britain’s Larger Moths 2013 report shows clearly that moths are in decline. The total number of larger moths recorded in the national network of Rothamsted trap samples decreased by 28% over the 40 years from 1968 to 2007.
Declines are worse in southern Britain, with a 40% decrease in total abundance, while there was no overall change in northern Britain (where declines have been offset by increases). The Rothamsted light-trap network is one of the longest-running and most wide-ranging insect population research projects ever conducted. Analyses of this data set, carried out by Rothamsted Research and Butterfly Conservation, together with information from the National Moth Recording Scheme and other sources, have been gathered together to produce the new report.
Forty-year national population trends were generated for 337 species of widespread and common moths. Two-thirds (227 species) show decreasing population trends over the 40 year study and over one-third (37%) of the species decreased by more than 50%.
Although the majority of trends are negative, 53 species (16% of the total) more than doubled their population levels (i.e. increased by at least 100%). Many of these species have also undergone dramatic range expansions, particularly northwards. Moth species that occur in both southern and northern Britain fared significantly worse in the south.
Ironically, against this backdrop of decline, many more moth species have arrived in and colonised Britain in recent decades than have become extinct here. Just since the year 2000, 27 moth species (macros and micros) have become resident in Britain and over 100 have been recorded here for the first time. In contrast, only a few species have become extinct, although this is much harder to measure.
The widespread decline of Britain’s moths is a clear signal of potentially catastrophic biodiversity loss caused by human impacts on the environment. Moths comprise a substantial part of Britain’s biodiversity and play important roles in food chains and as pollinators. Their decline will have knock-on effects on the birds, bats and mammals, which depend on them for food, and shows widespread degradation of our environment caused by habitat loss (e.g. to intensive agriculture, changing woodland management and urbanisation). Chemical and light pollution of the environment may also be having significant negative effects on moth populations, while climate change is causing both positive and negative impacts.