Despite widespread concern about declines in insects globally, a dire shortage of data on species numbers over time means it will be impossible to assess our progress towards biodiversity goals – and to implement effective conservation action.
That is the message from a team of international experts, led by the UK Centre for Ecology & Hydrology (UKCEH), who have calculated a Global Butterfly Index as a flagship indicator of species population trends that could provide an example for other groups of insects.
UKCEH ecologist Professor David Roy, senior author of the study, explained: “There are monitoring data on only about 5% of butterflies globally and around 1% of insects as a whole, which makes it extremely difficult to reliably assess how species are faring.
“As arguably the most popular insect group, we hope that the creation of indexes for butterflies will ignite public and political interest in biodiversity monitoring to guide action to maintain and improve habitats to support species.”
Important indicator
Butterflies play ecologically important roles within the food chain and as pollinators. They are sensitive to environmental change, providing an important indicator of the health of the countryside.
Furthermore, the study authors say there is a lot of potential for these charismatic creatures to engage the public and generate political interest in conservation of insect species.
More than 50 scientists from 23 different countries contributed to the perspectives paper in the journal Conservation Letters, collating 45,492 population time series from 1,055 butterfly species between 1990 and 2023 in 3,636 locations in 37 countries. They based their calculations on the Living Planet Index, a high-profile indicator that synthesises data on abundances of species of birds, amphibians, reptiles, fish and mammals to provide estimates on how biodiversity is changing over time.
Trends in butterflies are highly uncertain due to the sparsity of data but the study found an average decline of 24% over 25 years, with a larger decline of 63% for butterflies in North America.
Paper information
Riva et al. 2026. Addressing Gaps in Butterfly Population Monitoring to Catalyze Global Insect Conservation. Conservation Letters. DOI: 10.1111/con4.70037. Open access.
The study was partly supported by the INSPIRE project, funded by the Aberdeen Group Charitable Trust, and the Natural Environment Research Council through UKCEH’s National Capability Global Challenges programme.
