The State of Britain's Larger Moths 2021

The world is facing a biodiversity crisis. An estimated one million species are threatened with extinction¹, vertebrate populations decreased by 68% on average between 1970 and 2016² and globally agreed targets to reduce the pressures on biodiversity have not been met³.

The trends of insects, which make up at least 60% of all species on Earth4 and contribute vital and valuable ecosystem services, such as decomposition, pest control and pollination, remain poorly understood.

Recently, there has been great public concern about impending ‘insect Armageddon’, that is the catastrophic loss of insects across the whole world. This concern was ignited by the mass media reporting of recent studies such as those at sites in Germany5 and Puerto Rico6. Global and continental assessments for insects (and other invertebrates) have generally shown overall declines in abundance of terrestrial species7, but the available evidence is heavily biased towards Europe and North America. Long-term, continuous records of insect abundance and distribution are very rare elsewhere in the world, particularly in the tropics. Even where data exist, analyses are fraught with difficulty8. Thus, while there is considerable evidence for insect declines9, the data are insufficient to support extrapolated conclusions about the scale of the worldwide decreases across all insect groups¹0.

However, insect biodiversity trends are also complex. Headline figures of decline hide a multitude of winners and losers, as well as variation in trends between different geographical areas and time periods.

Sometimes there are conflicting signals from different measures of change (such as abundance and distribution). This complexity in insect trends is shown in analyses of moths from around the world¹¹. Overall declines in abundance or diversity, or both, have been reported at national, regional or site scales in several European countries including Finland¹², Germany¹³, Hungary¹4, the Netherlands¹5, Sweden¹6 and the United Kingdom (UK)¹7.

The previous State of Britain’s Larger Moths reports in 2006 and 2013 showed that total moth abundance had decreased, but that around one-third of widespread species had increased, and there was no overall change in the northern half of Britain¹8. In addition, more recent assessments of British moths over the same decades found that species had, on average, increased in distribution¹9. Similar findings have come from Finland, where moth species’ richness has increased but abundance has declined²0, and Hungary, where moth diversity has decreased but total abundance has not¹4.

The few studies of moth populations outside Europe also reflect this heterogeneity, with decreases in caterpillar abundance and diversity at a site in Costa Rica²¹, but no overall decline at monitored sites in Ecuador, Arizona (USA) or Missouri (USA)²².

Given this complex picture and the paucity of long-term data on moths in many parts of the world, The State of Britain’s Larger Moths 2021 report offers a new opportunity to assess patterns of biodiversity change for this ecologically important group using the most comprehensive moth datasets in the world.

All Butterfly Conservation Lepidoptera Moth Moths Report State of Nature Trends