More than three-quarters of the UK's native and migrant butterfly species have declined in the last 40 years - and climate change could be the culprit.
The alarming figures were released in a study jointly written by the Butterfly Conservation charity and the Centre for Ecology and Hydrology (CEH) in Oxfordshire.
Butterfly numbers have fallen across Europe, but the UK has been the worst affected, particularly the Southern part of the country.
The reasons for the dramatic decline in butterfly numbers are not fully understood, but it is believed that the combined effects of climate change, habitat destruction and increased use of pesticides and herbicides could have played their part.
Widespread butterfly species like the Wall, Essex Skipper and Small Heath are now some of the most severely declining butterfly species in the country. Overall, 76 per cent of the UK's butterflies have declined in numbers since 1975.
The Gatekeeper, a distinctive brown and orange butterfly that is one of the most abundant species in the UK, has experienced a 44 per cent drop in numbers in the last decade alone.
The report, The State of the UK's Butterflies 2015, warns that climate change has had "much more varied, subtle and worrying impacts on butterflies than had previously been realised".
However, while rising temperatures have been killing of native butterflies, some of the migrant species, like the Clouded Yellow, from north Africa and the Red Admiral, from Europe and Asia, are increasing in numbers.
TV presenter Chris Packham is the vice-president of Butterly Conservation, and said the decline of the UK's once-thriving butterfly population should "shame us all."
The BBC Springwatch presenter said: "As a society we are guilty of standing idly by as once common species, never mind the rarities, suffer staggering declines.
"We are finally facing the meltdown that was coming all along.
"There is a very, very urgent need to understand the reasons for the decline, which are likely to be complex."