Filling in the global information gaps on butterflies and other insects can help us to slow species declines and make sure they survive.

Around the world, many insects are declining, both in terms of diversity of species and numbers. Various studies have reported population declines of 1–2% per year. 

Butterflies are no exception. For example, numbers of grassland butterflies across Europe declined by 36% between 2011 and 2020, and butterflies in the US declined by an average of 1.6% per year between 1977 and 2018. 

Many of the existing insect data are taken from studies in temperate regions of the global north. The global south and tropics, meanwhile, contain some of the most biodiverse areas on the planet, but there are very few long-term butterfly or insect monitoring surveys taking place in these regions. This raises the question: what is happening to butterfly populations across the world as a whole?  

Addressing the data gap outside of temperate regions would make an important contribution to tackling the global biodiversity crisis. At a local scale, monitoring data can help people identify and act on the best conservation approaches. 

At a large scale, monitoring can help to influence government policies that affect biodiversity conservation. However, butterflies – and insects as a whole – are currently missing from most of the indicators we use to measure progress on global biodiversity commitments.

A black and white striped butterfly with a row of blue and back dots along the edge of its underwings
Striped Ringlet, Philippines. Photo by Holly Mynott.

Since the COP15 UN Biodiversity Conference in December 2022, governments have been working towards the Kunming-Montreal Global Biodiversity Framework to guide global action on nature. Within this, ‘Goal A’ includes the aim ‘to prevent species extinction’. Various indicators have been chosen to measure progress towards this goal. 

Most of these measure changes at an ecosystem or habitat level, but two include data on species-level population change. These are the Red List Index, which shows trends in species’ extinction risks, and the Living Planet Index, which is a measure of the overall state of global biodiversity, based on population trends. However, neither of these indicators currently include butterflies, or indeed any other insect. 

Insects’ exclusion comes down to a lack of global monitoring data. Addressing this omission is vital – how can the global community conserve butterflies and other insects if it doesn’t understand what’s happening to them?

A bright metallic green swallowtail butterfly resting on leaves with wings open
Emerald Swallowtail. Photo by Holly Mynott.

Thinking globally

The Global Butterfly Index project seeks to do exactly this. Of all insects, butterflies are the best placed to provide a global index to represent insect biodiversity. Their beauty and popularity, and the relative ease of distinguishing one species from another, means they are currently the best-monitored invertebrate group around the world.

Their short life cycles, limited dispersal ability, and sensitivity to weather patterns also mean they react quickly to changes in the environment. This makes them a good indicator species, both for the status of other insects and the overall health of the environment.

The first step is to gather existing datasets from around the world to incorporate into a preliminary Index – work is under way in this area. We’ll then look to support efforts to establish new butterfly monitoring schemes in under-represented countries, addressing the data gaps that currently bias index calculations towards Europe and North America.

A brown and orange striped butterfly feeding on purple flowers
Banded Orange Heliconian, Costa Rica. Photo by Holly Mynott.

We also aim to develop the existing ButterflyCount mobile app for use around the world. This app allows people to carry out different types of survey, whether a transect or a 15-minute count, and share their data. It’s currently available in Europe, Japan and Kenya. We’d like to expand it by adding further species, languages and survey methods, such as using fruit-bait traps, to use in the tropics. This will empower a global community of citizen scientists to monitor butterflies no matter where they live in the world.

As more countries around the world take up the cause, we’ll begin to gain a better understanding of what is happening to butterflies at a global scale. This will enable us to effectively target conservation action and help establish butterfly and insect conservation in global biodiversity policy.  

The Global Butterfly Index project is a collaboration between Butterfly Conservation, Butterfly Conservation Europe, De Vlinderstichting, IUCN Species Survival Commission on Butterflies and Moths, UK Centre for Ecology and Hydrology, and the Zoological Society of London.

Holly Mynott
International Officer at Butterfly Conservation