Britain’s moths provide a rare opportunity to assess trends for a species-rich insect group.
This is thanks to the Rothamsted Insect Survey (RIS), the longest-running, large-scale monitoring of insect abundance anywhere in the world, and the millions of moth occurrence records gathered through the National Moth Recording Scheme (NMRS).
The new State of Britain’s Larger Moths 2021 report1, published earlier this month, provides the latest in-depth assessment of the changing fortunes of these ecologically important insects, following previous reports in 2006 and 2013. Scientists from Butterfly Conservation, Rothamsted Research and the UK Centre for Ecology & Hydrology estimated long-term trends in abundance and distribution for Britain’s larger (macro-) moths from the RIS and NMRS datasets, respectively.
The total abundance of all larger moths caught in the RIS light-trap network in Britain over a 50-year period (1968-2017) decreased significantly by 33% (see plot). Splitting the data to estimate separate trends for northern and southern Britain, revealed significant declines in abundance in both halves, but a greater loss in the south (39% decrease) than in northern Britain (22% decrease). In contrast, a multi-species indicator created by combining the individual distribution (occupancy) trends for 511 species, showed that, on average, larger moths increased in extent in Britain by 9% over a 47-year period (1970-2016).
These overall summary measures obscure great variation in the fortunes of individual species over the past five decades. Of 427 species with sufficient RIS data to calculate long-term population trends, 175 species (41% of the total) had decreased significantly, 42 species (10% of the total) had increased significantly and the remaining 210 species (49% of the total) had non-significant trends. Thus, four times as many moth species declined in abundance as increased. However, more species increased in distribution in Britain than declined since 1970; 165 species (32% of the 511 species with sufficient NMRS data) showed significant distribution declines, while 187 (37% of the total) showed significant increases and 159 species (31%) had non-significant distribution trends.
While the destruction and deterioration of wildlife-rich habitats likely remains the main driver of declines among Britain’s moths, there are clear signs that climate change is exerting a major influence on species trends. A number of species adapted to cooler conditions in northern and western Britain appear to be retreating, including Grey Mountain Carpet Entephria caesiata (81% decrease in distribution 1970-2016), Brindled Ochre Dasypolia templi (76% decrease), Red Carpet Xanthorhoe decoloraria (62% decrease), Grey Chi Antitype chi (57% decrease), Autumn Green Carpet Chloroclysta miata (38% decrease) and Glaucous Shears Papestra biren (38% decrease). At the same time, and in keeping with other taxonomic groups2, many other moth species are expanding northwards, seemingly in response to climate change, with increases in distribution and sometimes also abundance. On average, the northern limit of southerly-distributed moth species shifted northwards at a rate of 5km per year over the period 1995-2016, and 71% of 487 larger moth species assessed had spread north.
Extinctions are still occurring but the rediscovery of some moth species and natural recolonisation by others (such as the Clifden Nonpareil Catocala fraxini) has reduced the number believed to have been lost from Britain since 19003. The total now stands at 51 species (including micro-moths) and the report highlights three additional species as potentially extinct: Aproaerema albipalpella, Scythris siccella and Pale Shining Brown Polia bombycina. On the other hand, many more moth species have colonised Britain. Since 1900, 137 moth species (including micro-moths) have become (and remain) established, including 53 this century. Some have arrived naturally, expanding their European range in response to climate change, while others have been unwittingly imported through the global trade in plants.
Overall, the report confirms continued rapid change to Britain’s larger moth fauna. But it is a complex picture. While substantial numbers of moths are expanding their distributions, and new species colonising our shores, there is also clear evidence of significant declines. The reduced abundance of common and widespread moths may generate cascading impacts on many other organisms through trophic networks and the disruption of pollination services.
This assessment of the state of Britain’s moths was only possible thanks to the hard work and expertise of the moth recording community and, in particular, the volunteer County Moth Recorders. The Rothamsted Insect Survey, a National Capability, is funded by the Biotechnology and Biological Sciences Research Council (under the Core Capability Grant BBS/E/C/000J0200) and Natural England provide financial support for the National Moth Recording Scheme and have contributed to the production costs of the new report.
Associate Director Recording and Monitoring, Butterfly Conservation
- Fox, R., Dennis, E.B., Harrower, C.A., Blumgart, D., Bell, J.R., Cook, P., Davis, A.M., Evans-Hill, L.J., Haynes, F., Hill, D., Isaac, N.J.B., Parsons, M.S., Pocock, M.J.O., Prescott, T., Randle, Z., Shortall, C.R., Tordoff, G.M., Tuson, D. & Bourn, N.A.D. (2021) The State of Britain’s Larger Moths 2021. Butterfly Conservation, Rothamsted Research and UK Centre for Ecology & Hydrology, Wareham, Dorset, UK.
- Mason, S.C., Palmer, G., Fox, R., Gillings, S., Hill, J.K., Thomas, C.D. & Oliver, T.H. (2015) Geographical range margins of a wide range of taxonomic groups continue to shift polewards. Biological Journal of the Linnean Society 115:586–597. doi:10.1111/bij.12574
- Parsons, M.S. (2020) The changing moth and butterfly fauna of Britain – the second decade of the twenty-first century (2010–2019). Entomologist’s Record and Journal of Variation 132:53–62.