A study1 led by Butterfly Conservation scientists, in collaboration with Rothamsted Research, has revealed complex patterns of winners and losers among Britain’s larger moths. This new research builds upon the creation of a ‘traits’ database2 that draws together a wealth of information about the life cycles and ecology of our butterflies and larger moths.
The new study relates the characteristics of moth species contained in the traits database to long-term abundance and distribution trends calculated from the Rothamsted Insect Survey and National Moth Recording Scheme, respectively. These huge datasets mean that the resulting population trends are the most robust ever produced for moths, allowing us to look at associations with species characteristics, such as forewing length, habitats used or overwintering stage, in a more comprehensive way than has been possible before.
Our analyses revealed many conflicting results, where a characteristic was significantly correlated with abundance trends but not with distribution trends or vice versa. Reviewing previous similar studies of moths from across Europe shows that such inconsistencies are common, leading us to conclude that traits-based approaches have limited value in predicting population declines for less well studied species groups and regions. We suggest that these inconsistent results are rooted in the complex drivers of population change, as well as incomplete knowledge of some traits.
Despite the widespread inconsistences in moth traits studies, our analyses did produce largely congruous results for traits relating to dietary and habitat breadth. Generalist moths with a flexible life history – those that have a wide range of caterpillar foodplants and more than one generation per year – are faring better than more specialised species – those that have just one or a few foodplants and only one generation per year. The numerous and wide-ranging human impacts on the environment, such as habitat loss and degradation, pollution and climate change are likely to favour generalists, like the increasing Vine’s Rustic, rather than specialists, such as the declining Bilberry Pug.
Our analyses also revealed that woodland moths are faring relatively well, whereas moths associated with moorland show stronger declines than those breeding in other habitats. In response to this finding, Butterfly Conservation have instigated further research in an effort to determine why moorland moths such as Clouded Buff and Grey Mountain Carpet are struggling. Possible factors include the increasing frequency of moorland burning and the impacts of nitrogen pollution on plant communities. Woodland moths, conversely, may be responding positively to an overall increase in woodland cover in the UK in recent decades. Climate change is also likely to be factor for both groups of species, threatening moths adapted to colder conditions in upland areas but enabling some southern species to spread further north.
Moths with caterpillars that feed on lichens and algae also tend to be faring well, a finding consistent with previous studies. It is likely that lichen-feeding species, such as the various footman moths, Marbled Green and Brussels Lace, have benefitted from the recovery of lichens due to the Clean Air Acts. Species that uses grasses as caterpillar foodplants have increased on average, while those using wildflowers have tended to decline.
Our study would not have been possible without the dedicated efforts of the moth recording community, which contributed an astonishing 24 million records to our analyses from the National Moth Recording Scheme.
George Tordoff, Senior Ecologist & Emily Dennis, Senior Ecological Statistician
1. Tordoff GM, Dennis EB, Fox R, Cook PM, Davis TM, Blumgart D & Bourn NA (2022). Inconsistent results from trait-based analyses of moth trends point to complex drivers of change. Biodiversity and Conservation (2022):1-20. DOI: 10.1007/s10531-022-02469-8
2. Cook PM, Tordoff GM, Davis TM, Parsons MS, Dennis EB, Fox R, Botham MS & Bourn NA (2022). Traits data for the butterflies and macro‐moths of Great Britain and Ireland. Ecology 103: e3670. DOI: 10.1002/ecy.3670