"It's been a bit of a disastrous summer for butterflies," said Dan Hoare, director of conservation at the Butterfly Conservation, a wildlife charity.

"We've gone from this situation where seeing a butterfly outside on a sunny day was a normal part of our everyday lives to that being a rare event," he told AFP.

Butterfly Conservation runs the "Big Butterfly Count", an annual census carried out by tens of thousands of volunteers across the UK.

This year's count, which aims to gauge the health of the environment, returned the lowest numbers in 14 years -- down 81 percent for species counted compared to 2023.

A third of species observed were at their lowest level ever.

Experts blame a wet summer but also changes in land use and agricultural practices, including pesticides, as well as global warming.

Butterfly Conservation -- whose president is the television naturalist David Attenborough -- has declared a "butterfly emergency" to underline the threat.

This year's decline in numbers is part of a longer-term trend: 80 percent of butterfly species in the UK have declined since the 1970s.

Half are also formally listed as "threatened" or "near threatened" with extinction on the International Union for Conservation of Nature's Red List.

Hoare said action was needed before it was too late because butterflies' disappearance threatened biodiversity.

The charity wants greater protection for butterfly habitats and a ban on "butterfly killing" neonicotinoid insecticides.

The insecticides, which are also toxic to bees, are used widely in crop production, domestic gardens and golf courses, and as flea medication for pets.