THEY will be out, as they are every summer, beneath the canopy of high trees, in Fermyn Woods in the heart of the Rockingham Forest. They are the secret members of a quaintly named society called the Purple Empire.

They and I have been out, and online, seeking delicacies for the planned annual breakfast. Chief items on the menu will be the most pungent and malodorous exotic oriental shrimp paste that members of the Empire can find.

Popular brands are Big Cock shrimp paste and Thai Boy shrimp paste.

The Royal guest of honour at the morning feast is Britain’s second largest, and most spectacular butterfly — the aptly named Purple Emperor (Apatura iris). Only male butterflies attend the feast.

Spectacular the emperor might be, but it is also spectacularly difficult to observe. The colourful males flit high in the tree tops waiting to lure a dull female virgin to mate.

Generations of amateur, but skilful lepidopterists have discovered that the gloriously coloured male butterflies can be lured down into camera range by things like rancid pickled mud fish, stinking mature cow pats or those curiously named shrimp pastes. It seems that what is required are really high levels of sodium and other salts and to be really smelly.

There are several reasons why the Fermyn Woods are one of the best places to see Britain’s second biggest butterfly — only the Swallowtail (Papilio machaon britannicus) is bigger.

The Emperor is large and dark with white banded wings. Males have an iridescent purple sheen to their upper wings, while females are brown and quite dowdy. Males are the size of a small bird.

Fermyn Woods are marshy and full of Goat Willow (Salix caprea) and Grey Willow (Salix cinerea) trees, the favourite food plants of the purple emperor’s caterpillars.

It was in these woods that one of our greatest countryside writers, Denys Watkins-Pitchford, who wrote under the name of BB, found much of his inspiration.

I have written about BB as one of my favourite countryside writers. It was the curious pen name of Watkins-Pitchford. The pen-name comes from the size of lead shot wildfowlers used to bring down a wild goose, and BB was an enthusiastic wildfowler.

BB spotted his first purple emperor when very young. Sadly by the 1960s, insecticide spraying against the Oak Torix moth had led to the emperor’s local extinction.

BB was determined to bring the insect back to the woods near his Northamptonshire home. He made it a personal crusade. He taught himself how to gather eggs successfully and hatch them in huge muslin cages in his garden. He released the mature emperors back into Fermyn Wood close to his home.

Watkins-Pitchford was born in 1905 in Lamport, Northamptonshire. A country vicar’s son he spent his boyhood wandering through the fields, developing his love of the outdoors.

At 15, he left home for Northampton School of Art. There he won a scholarship to Paris. Back in London he entered the Royal College of Art and in 1930 he became an assistant art master at Rugby Public School where he taught for 17 years.

While still teaching he started his career as an author and an artist. He wrote under the name BB but used his real name as the illustrator of his and other authors’ books. He also wrote and illustrated hundreds of magazine articles.

He produced 60 books. There were award-winning children’s books; countryside books; books on wildfowling, shooting and fishing and on countryside travels with his caravan.

Wild Lone: The Story Of A Pytchley Fox and Manka, The Sky Gypsy is the tale of an albino goose. Both are masterpieces.

In 1974, his wife, Cecily, became unwell after working in their garden while a farmer was spraying his fields next door. She died a few weeks later. It confirmed BB’s long-held views on the harm insecticide poisons were doing to his beloved wildlife. The author constantly battled to preserve many species against the insecticide sprays so common in the 1960s and ’70s.

In his writing BB would talk sadly of the changes that had affected the countryside he loved. Woodlands and hedgerows of his youth had been grubbed up. He believed there were less than half the numbers of birds than when he was a boy.

It is, of course, true that like many countrymen of the time, BB shot wild birds, but always for the pot. He never enjoyed the formal shoots that killed hundreds of pheasants in a day for so-called sport. He rarely shot more than one or two geese and in his later books he attacked the slaughter of large numbers of geese by unscrupulous commercial gunners.

The purple emperor is a magnificent and elusive insect — nicknamed “His Majesty” by butterfly fans — it spends most of its time high in the woodland canopy feeding on aphid honeydew. Only occasionally will it flutter down to feed on tree sap or, in the case of the male, animal dung, carrion, or even that tempting shrimp paste. Scientists believe this extra diet provides the emperor with much-needed sodium salts and other minerals.

A male emperor is, without doubt one of the most beautiful of all of the butterflies found in the British Isles. Viewed from some angles the wings look black with white bands. Then as the sunlight catches the wing scales they light up with an amazing regal purple sheen. The female is a deep brown almost dowdy.

If you want to spot one the best time is early morning or in late afternoon. It is then that the males come down to the ground to feed on moisture from damp earth and animal droppings. The males will sometimes spend over an hour feeding in the same place.

They are often found in woodland car-parks and seem to love landing on wet muddy cars. Strangely they also enjoy sweaty humans and often land on the butterfly enthusiasts themselves — but never on Prince Andrew.

The males tend to congregate in very large oak trees that the butterflies have used for generations. From such a high point, perhaps on the top of a hill, the males wait to intercept passing females. They vie for the best and highest perches and battle it out with purple wings flashing in the sun. It is a sight you will never forget.

When a virgin female flits by the pair fly off to the high canopy to mate. Mating over, she flies down to earth while he returns to his high perch ready for another chance to pass on his DNA.

Northamptonshire’s Fermyn Woods have a rich working-class history. They were the location of a ministry of labour camp that opened in 1928. Its purpose was to judge the suitability of unemployed young men planning to emigrate to Canada and work in agriculture.

Just one year later in 1929, the worldwide slump had put and an end to dreams of a new, affluent life on Canada’s prairies. However, the centre continued its work, and housed up to 200 young jobless men. They worked on land clearance and similar heavy labour.

The establishment closed as the war clouds gathered. Today Fermyn Woods still gives disadvantaged youngsters a taste of forest work in the open air and just occasionally these young people will turn their eyes skyward to catch a glimpse of the impressive Purple Emperor — all thanks to a man called BB.