Scientists at the University of York have revealed that the 1976 drought is the worst extreme event to affect butterflies and moths in the 50 years since detailed records began.
The summer of 1976 saw standpipes in the streets and billions of seven-spot ladybirds swarming in search of food.
Since then, the UK has warmed by a full degree Celsius and experienced numerous bouts of extreme weather, from heavy rainfall and flooding to heatwaves and drought; yet no single year has caused so many butterfly and moth species to crash simultaneously.
"It was the culmination of a two-year event."
said Dr Phil Platts, Postdoctoral Research Associate in York’s Department of Biology and co-author of the study.
"Hot and dry conditions stretched back to the spring of 1975.
The study also looked at the impact of extreme weather on birds, determining that the cold winter of 1981-82 had the biggest effect on their numbers.
"This seems to be truer of short-lived species that can multiply rapidly, like butterflies and moths, than of the birds we studied."
said Professor Tom Brereton, co-author and Head of Monitoring at Butterfly Conservation.
However, global warming is projected to increase the frequency of extreme weather events such as heatwaves and drought, and it is likely that some of these will generate even greater population changes than we have seen so far.

The summer of 1976 saw standpipes in the streets and billions of seven-spot ladybirds swarming in search of food.
It was the hottest English summer since records began over 350 years ago – the mercury topped 32 °C for 15 consecutive days across much of southern England, and some regions received no rain for 45 days straight.
Since then, the UK has warmed by a full degree Celsius and experienced numerous bouts of extreme weather, from heavy rainfall and flooding to heatwaves and drought; yet no single year has caused so many butterfly and moth species to crash simultaneously.
"It was the culmination of a two-year event."
said Dr Phil Platts, Postdoctoral Research Associate in York’s Department of Biology and co-author of the study.
This was initially good for butterflies and moths, and their numbers boomed.
The study also looked at the impact of extreme weather on birds, determining that the cold winter of 1981-82 had the biggest effect on their numbers.
"This seems to be truer of short-lived species that can multiply rapidly, like butterflies and moths, than of the birds we studied."
However, global warming is projected to increase the frequency of extreme weather events such as heatwaves and drought, and it is likely that some of these will generate even greater population changes than we have seen so far.
Professor Chris Thomas, senior author in York’s Department of Biology, said: "If we want to avoid a future super-heated drought that will put 1976 in the shade, then we need to address the root cause of climate warming – greenhouse gas emissions.

"Their caterpillars defoliated 27,000 acres in Rhode Island in the spring of 2015, but even though we had winter moths everywhere last year and I saw a zillion eggs, they caused almost zero defoliation."
Faubert believes last year’s strange winter and spring weather negated what she expected to be a dire season for winter moth defoliation.
Winter moth eggs typically hatch during a warm spell in April, but last year they began hatching during a warm period in late March.
With little defoliation occurring last year from winter moths, Faubert said it’s possible that there will be fewer adult moths flying around in the next month.
"Defoliation is very stressful to trees," Faubert said.
The females crawl up tree trunks to lay their eggs.
In an experiment she conducted last year, Faubert placed two tree bands, separated by about a foot, around one tree.
One strategy Faubert is deploying to control winter moth populations is the release of a tiny parasitic fly that lays its eggs on tree leaves.
When the winter moth caterpillar consumes the eggs while eating the leaves, the eggs hatch inside the caterpillar and the fly larva eat it from the inside out.
Faubert released the flies in seven locations in Rhode Island between 2011 and 2015, and she hopes to soon see signs that it is beginning to work.