It is one of the most beautiful – and most elusive – butterflies ever to be found in Britain.
And after decades of decline, the magnificent Purple Emperor is set to make a comeback in record numbers this summer, thanks to May’s unusually warm weather.
‘This year will be amazing and possibly the best this century,’ said nature writer Matthew Oates, who has been obsessed with the species since childhood.
He even runs ‘safaris’ to try to record sightings of the insect, often armed with dung or a very stinky camembert to lure it from the treetops.
The elusive Purple Emperor Butterfly is set to comeback to the UK in record numbers this summer after high temperatures in May
Because for all its beauty, the Purple Emperor, affectionately dubbed His Imperial Majesty, is drawn to the distinctly unlovely odours of smelly cheese, dog poo, human sweat and fish paste – possibly attracted to the salts and minerals they contain.
Once ubiquitous, its population in Britain declined dramatically after the First World War when its favourite habitat, broad-leaved willows, were destroyed as pernicious weeds, but it has slowly been making a return.
And as the season to spot them starts as early as today, as they emerge from their pupae, the signs are good for a bumper summer.
‘I monitor the Purple Emperor larvae sites and usually about 85 per cent are lost to predators, but this year it’s been less than 50 per cent,’ Mr Oates said.
‘It does have periodic abundant years but this year, I believe, will be amazing and possibly the best this century.
'During hibernation, larvae live on twigs and are eaten by blue tits, and small mammals, but with the fine spring, the larvae like hot weather and have developed well and survived.
‘This butterfly is bucking the trend and I believe there are colonies of Purple Emperor in places beyond imagination.’
By which he means locations such as Herefordshire, Monmouthshire and Yorkshire, beyond the usual heartland in the South of England.
The beautiful butterflies are drawn to distinctly ugly smells, namely smelly cheese, dog poo, fish paste and human sweat
Common spotting sites include the New Forest, Surrey, Sussex, Hampstead Heath in London and Epping Forest.
Among those preparing to go in search of the elusive insect, whose wingspan can reach 4in, is David James, 42, from Northamptonshire.
‘Purple Emperor season is a pilgrimage, the Glastonbury of the butterfly world,’ he said.
‘You have to wear purple because it brings you good luck. It’s British eccentricity at its finest.’
From certain angles, the male butterfly appears to have black wings intersected with white bands, but when bathed in sunlight an iridescent purple sheen appears as light is refracted through the scales of the wing.
Mr Oates, author of His Imperial Majesty: A Natural History Of The Purple Emperor, recommends travelling to areas where colonies are known to exist and putting out a smelly meal between 8.30am and midday.
The charity Butterfly Conservation said this summer is expected to be the best for all species since 2011, with early sightings of 53 of the UK’s 59 resident and migrant types of butterfly already logged.
The public can record sightings at bigbutterflycount.org.