The discovery of the black hairstreak butterfly is thrilling

This is the discovery in the past month of a new and very rare butterfly which has for centuries been confined to one small and closely guarded colony in the Midlands.

Butterfly expert David Cook has found a large and thriving colony of the black hairstreak butterfly on Ditchling Common Country Park in East Sussex, north of this week’s walk.

The insect was for decades the special interest of Miriam Rothschild, of the famous banking family, who even ran a pub called The Black Hairstreak in honour of the rarity. She devoted her life to safe-guarding wildlife and was partly responsible for the butterfly’s conservation and preservation.

It has always been the mecca for lepidopterists who wanted to add it to their list of almost sixty species of UK butterflies which they had watched and photographed. I tried to see it at one time back in the 1970s but was unsuccessful and by the time the news reached me of the Sussex discovery it was too late for this year as the tiny butterfly had already completed its life-cycle for this year.

It will reappear next June when this year’s eggs have hatched and developed as caterpillars and then pupated, to hatch into the final stage of winged insects after some 18 days.

That will be something to look forward to. So how has this rarity suddenly hopped a hundred miles south? The species, like all the other hairstreaks, is not adventurous and generations tend to stay on the same tree year after year for their breeding cycle, but scientists have found that the population could move 100 yards each year. The black hairstreak needs mature blackthorn bushes and trees as nursery for the caterpillars.

Ditchling Common has a kilometre stretch of mature sloe bushes which are growing on a strip of Wealden clay – the type of geology found at its original station between Oxford and Peterborough. Were the caterpillars introduced from the Midlands?

There is no record of this happening, but if so, that could have occurred 40 years ago for the colony to have grown to its present size.

Today it is illegal to introduce species to an SSSI and it is also illegal to collect specimens without a licence from Natural England. At least 98 adults were counted this year.

If you go to see them next year look on bracken fronds which is where they like to sunbathe and sip honeydew. They also need a large oak to gather for their courtship displays high above the ground, just like the purple hairstreak does.

I am indebted to Chichester wildlife photographer Brian Henham for his picture of a female black hairstreak taken at Ditchling Common Country Park last month.