1. Brereton, T., Roy, D. B., Middlebrook, I., Botham, M. & Warren, M. The development of butterfly indicators in the United Kingdom and assessments in 2010. Journal of Insect Conservation 15, 139–151 (2011).
2. Thomas, J. A. Monitoring change in the abundance and distribution of insects using butterflies and other indicator groups. Philosophical Transactions of the Royal Society B: Biological Sciences 360, 339–357 (2005).
3. Dennis, E. B., Morgan, B. J. T., Roy, D. B. & Brereton, T. M. Urban indicators for UK butterflies. Ecological Indicators 76, 184–193 (2017).
4. Wepprich, T., Adrion, J. R., Ries, L., Wiedmann, J. & Haddad, N. M. Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA. PLoS ONE 14, 1–21 (2019).
5. Van Swaay, C. et al. European red list of butterflies. Publications Office of the European Union (2010). doi:10.2779/83897.
6. Sánchez-Bayo, F. & Wyckhuys, K. A. G. Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation 232, 8–27 (2019).
7. Wagner, D. L. Insect declines in the anthropocene. Annual Review of Entomology 65, 457–480 (2020).