Climate change is causing a striking butterfly from southern Europe to appear in record-breaking numbers across the south of England, wildlife charity Butterfly Conservation can reveal.

More than 50 Long-tailed Blue butterflies and hundreds of the butterfly’s eggs have been discovered over the last few weeks, which could result in the largest ever emergence of the butterfly in UK history.

Experts believe rising temperatures are behind the influx, with sightings of the butterfly coming in from Cornwall right across to Kent, as far north as Suffolk and even into Surrey – where the Long-tailed Blue hasn’t been seen since 1990.

Typically, only a handful of these exotic migrants from the Mediterranean reach the UK each summer, but this is the third time in six years that the butterfly has arrived in vastly increased numbers and 2019 looks set to surpass the previous peaks witnessed in 2013 and 2015.

Butterfly Conservation volunteer and Long-tailed Blue expert, Neil Hulme, said:

“These butterflies have crossed the Channel and are laying eggs in gardens, allotments and anywhere you can find Broad-leaved Everlasting-pea and similar plants, which the caterpillar likes to feed on.

“We’ve never recorded this many migrant adults before – it’s completely unprecedented. In only a few days, I’ve found more than 100 eggs in Sussex alone and the butterfly has been seen in Cornwall, Somerset, Devon, Dorset, Hampshire, Kent and Suffolk. We’ve even had a sighting in Glamorgan in South Wales.

“What’s really exciting is that the Long-tailed Blue has gone further inland than it did in 2013 and 2015, with at least three confirmed sightings in Surrey, where the butterfly hasn’t been seen for 30 years.

“The adults will keep laying eggs and in September and October we’ll see the first British-born offspring emerging. I strongly believe this will take the total number seen this year to well over a hundred, breaking all previous records for this butterfly in the UK.”

The Long-tailed Blue has previously been considered a very rare visitor to the UK, despite being abundant across southern Europe, Africa, Asia and Australia.

Long-tailed Blue (male) - Bob Eade
Long-tailed Blue (male) by Bob Eade

The butterfly was seen for the very first time in Britain in 1859, but over the next 80 years only 30 adults were recorded here. Significant influxes occurred in 1945, 1990 and most recently in 2015, but none of these equalled the invasion of 2013, when 109 sightings were recorded between July and October.

Neil added:

“This is one of the world’s more successful species of butterfly. It may be small, but it’s a very powerful flyer, capable of crossing mountain ranges and seas.

“In hot weather it can go through its entire life cycle in just over a month, which is half the period taken by many species. The caterpillar grows up inside the flowers and pods of peas and similar plants, hidden away from predators. It has the full toolkit for world domination.”

The butterfly gets its name from the wispy ‘tails’ on the trailing edge of each of its hindwings, which flutter in the breeze. Adjacent eye spots fool birds into thinking this is the head of the butterfly, allowing it to escape any attacks unharmed.

Long-tailed Blue (female/underwing) - Iain Leach
Long-tailed Blue female

The male is a striking violet-blue colour, while the female is a mix of duller blue and brown. The underside of both sexes is a sandy brown colour crossed by numerous white, wavy lines.

Dr Dan Hoare from Butterfly Conservation said:

“With unprecedented numbers of Long-tailed Blues and UK sightings of other rarities, like the Bedstraw Hawk-moth and Queen of Spain Fritillary butterfly, 2019 is certainly turning out to be an exciting year for immigrant species.

“The Long-tailed Blue is still a way off from becoming a resident butterfly in this country, as it can’t survive our winter. However, what we’re seeing this year confirms the butterfly is extending its geographical range northwards in response to climate change – so we can look forward to seeing this beautiful little butterfly more regularly.

“Our rapidly changing climate brings positives for some expanding species, while others may find it much harder to adapt and keep pace with the changes. Butterflies, moths and other insects respond quickly to environmental change, providing an indicator of the impacts of a warming climate on the natural world.”

Please report any Long-tailed Blue sightings to your local county butterfly recorder, or through the free iRecord Butterflies app.