A thriving colony of Sussex Blue butterflies

Chalkhill Blue butterfly''Picture Brian Henham
Chalkhill Blue butterfly''Picture Brian Henham

A FEW years ago I took Chichester MP, Andrew Tyrie, to see the chalkhill blue butterfly colony near the city at its downland habitat. He has a life-long interest in the countryside and in butterflies in particular, and was pleased that one of our Sussex national nature reserves, funded by the government, had such a thriving colony of these lovely insects.

Chalkhill Blues fly in late July and August. We looked at the food plant which the butterfly needs to survive, the horse-shoe vetch.

He was amazed to be told that the colony near Chichester exists on about two square metres of the plant. It really showed him how incredibly vulnerable the species is to disturbance.

Fortunately we had picked a good warm day and the chalkhills were flying about nicely, all of them confined to about a quarter of an acre of land. They are not adventurous and never travel.

If their two square metres of horse-shoe vetch is destroyed, for instance by a camp fire or is overgrown with brambles, that is the main colony gone into extinction. This year the blue butterflies were out and about again but not in the large number we had last year, when 56 were counted. The photograph this week was taken by wildlife photographer Brian Henham, who can make a far better job of catching butterflies in his digital lens than ever I could. Thanks, Brian.

This picture shows a male chalkhill blue with its pale blue wings and prominent black and white border. This insect is different to all the other blues we have on the downs which are a deeper blue or in some cases , soot coloured like the small blue.

I always think the chalkhill blue resembles the lovely heron’s egg blue of a summer evening sky when the sun is sinking down beyond the Isle of Wight. In contrast the common blue and the adonis blue have that azure of a noonday sky.

The chalkhill blue we saw this year were all in the act of pairing off to mate. Each pale blue male had a sooty brown female in his sights and was following her at the standard distance of about four or five inches.

Wherever she flew, the male followed. This would have gone on for a day or two before the females were ready to join.

All fifty plus insects were using the same old Bronze Age earthwork to display to each other, which they have used every year, probably way back in time. It provides a nice southerly front so they are sheltered and warm.

Masses of small downland flowers grow on this bank to keep them topped up with carbohydrates. It is as pretty a picture as you could hope to see in nature.

When mated a week later, all the females are drawn to that two square metres of horse-shoe vetch, on which they lay all their eggs. The creche is essential, small though it is. It was a good object lesson for the MP, one which helps secure a small but vital part of our biosphere. That’s where our biosphere should be, in the bank.