Last year was the seventh worst on record for butterflies in Britain, and for two declining butterfly species it was their worst since records began.
Fewer grayling and grizzled skippers took to the skies than in any year since the scientific monitoring of butterflies began more than 40 years ago.
The annual UK Butterfly Monitoring scheme revealed that seven of the worst 10 years for butterflies have occurred this century. While long-term falls in butterfly populations have been caused by habitat loss, scientists attribute the dramatic recent decline to climate change, pesticides such as neonicotinoids and nitrogen pollution.
While it was hoped that a brighter spring in 2017 would see butterfly populations bounce back after the virtually butterfly-less late summer of 2016, many of Britain’s 59 native species, both rare and common, suffered further falls. Grizzled skipper numbers have more than halved since the 1970s while the grayling’s population has shrunk by 63% in the last decade. The large white – once so common it was a pest – fell by 19% in 2017.
There was some good news, with two species enjoying long-term increases once again experiencing good summers: the red admiral was up by 78% compared to 2016 and the comma rose by 91%. A warm spring and targeted conservation management for a rare butterfly, the pearl-bordered fritillary, also reaped dividends, with a 57% increase on 2016.
“Butterflies are at a low ebb, and going from one bad year to another, not helped by the weather which is all over the place,” said Prof Tom Brereton, head of monitoring at Butterfly Conservation. “A lot of climate change research has focused on average increases in temperature, which should be beneficial to many butterflies but the variable and extreme weather that comes with climate change is having a negative effect and disrupting butterflies.”
Increased nitrogen deposition – via agricultural fertilisers but also pollution from motor vehicles – is highly likely to be causing the disappearance of butterflies such as the grayling and grizzled skipper, according to Brereton.
The caterpillars of such species feed on plants which are easily swamped by more vigorous grasses, which thrive in high-nitrogen conditions.
“The conservation management has not really changed on sites such as nature reserves but the vegetation has subtly changed – it’s grassed over, or become taller and shadier,” said Brereton. “It’s not surprising that insects like the grayling, wall brown and grizzled skipper are struggling.”
Brereton led research which last year uncovered surprisingly high declines of butterflies in urban areas, where vehicle pollution has caused nitrogen levels to soar.
“There does seem to be a correlation between butterflies that have a low nitrogen status and their declines in areas of high nitrogen deposition,” said Brereton. “There is some evidence of this from the Netherlands but more research is needed.”
Butterflies have been scientifically recorded since 1976 by thousands of volunteers for the UK Butterfly Monitoring Scheme, a partnership between Butterfly Conservation, the Centre for Ecology & Hydrology, the British Trust for Ornithology and the Joint Nature Conservation Committee.
The 10 worst years for butterflies (since scientific monitoring began in 1976)
1.2008
2.1981
3.2012
4.2016
5.2007
6.1977
7.2017
8.2001
9.2002
10.1988
