Dr Richard Fox, Associate Director of Recording and Research at the charity Butterfly Conservation, who compiled the figures, said that over the past 20 years he had typically received reports of 39 species by the end of May, so 53 this year is “amazing”.
He said: “Last year, for example, only 43 butterflies had put in an appearance by this point and the only other year to come close to the current total was in 2011, when 50 species had started to emerge by May 31.”
The sightings, which are made by volunteers, are displayed on Butterfly Conservation’s First Sightings website and the charity said it showed some “extremely early” dates for particular species this spring.
Volunteer at Butterfly Conservation Yorkshire and researcher at Hull University, Dr Callum Macgregor, said they had seen the first sightings in Yorkshire of the Northern Brown Argus on May 20, when they would normally expect it to be seen in late June. This made it the earliest emergence for this species on record.
Dr Macgregor, whose work has included studying the life cycle events of butterflies, said the early emergence is tied to the exceptionally warm weather the country has experienced and were indictors of climate change.
He explained that butterflies are able to adjust their emergence dates to suit the UK weather which ensured they remain in sync with the plants their caterpillars need to feed on.
“Butterflies have definitely emerged earlier this year and this is a bio indicator of climate change,” Dr Macgregor said.
“The early emergence of butterflies and moths in Britain over recent decades in response to climate change isn’t necessarily beneficial,” Dr Fox added.
“Recent research shows that emerging earlier leads to larger populations of species that have more than one generation each year. In such species, the earlier emergence of the first generation leads to greater abundance in the second brood.
However, for species that only have one generation each year, this positive effect on numbers was not found.
“Indeed, for some, more specialised species, there was a negative impact – earlier emergence led to reduced population size.”
Across the country species such as the Ringlet butterfly, which would not normally be seen before June 8, was spotted on May 24. The White-Letter Hairstreak, normally seen on June 11, was spotted on May 29 and the rare Large Blue, successfully reintroduced to Britain in the 1980s, made its earliest ever appearance this year.
However, the hot weather also impacts on the caterpillar’s food source with a lack of rainfall meaning a number of plants die back which can lead to starvation. Dr Macgregor said this was particularly difficult for species whose caterpillars only fed on one or two types of plant.
As well as informing the charity of butterfly numbers, Dr Macgregor said the data collected by volunteers also gave a good indication as to the health of other insects and birds. With caterpillars being an important food source and link in the food chain, any decline in numbers had an impact.