RICHARD WILLIAMSON: Butterfly season closes

YET another butterfly season draws to its close and summer slips into autumn.

This was the 40th year that I have completed the Butterfly Monitoring Scheme (BMS) which today has more than 2,000 volunteers covering every habitat through the UK.

By walking exactly the same route on the finest day of the week from April to October, we can provide an accurate sample of butterfly populations during the year and how this changes from year to year, decade to decade.

My sample walk covers nearly five miles over the whole of Kingley Vale, three miles NW of Chichester.

The 40-year graph there shows a peak every seven years for the total number of butterflies I see three metres either side of my path, and when plotted it looks like a hospital heart graph, though it is seven years apart instead of one second.

This year has been an average low of 4,500 butterflies, with a peak expected in three years’ time.

The last peak was in 2011 with more than 7,000 butterflies counted. The highest number I ever recorded was in 1991 with nearly 12,000, while the worst-ever was 2001 with just over 2,000.

The commonest butterfly is the meadow brown.

This is such an obvious insect that it hardly needs description. It is even found in the big London parks because its caterpillars feed on grass.

This year the next most common was the ringlet, which is a sooty brown family member and often difficult to tell apart from some male meadow browns which are also very dusky.

What people tend to generalise as ‘cabbage whites’ can be any one of four whites – large, small, green-veined, and wood. People even lump the female brimstones as ‘whites’.

All of these have not done at all well, except the brimstone.

The blues have not done well either, although some people have seen swarms of silver-studded blues on the heathery commons.

My most exciting find was a clouded yellow, right at the end of the season, the only one of the year, which I managed to photograph as it sucked sugar out of a hardhead flower.

Close by was a brimstone, also stoking up energy as shown here. This brimstone will by now be hibernating in the thick ivy on oak trees, and with luck will fly again next March or April.

So what is happening to the butterflies of the Downs? In general, the populations are stable.

There are some increases, notably with marbled whites and small skippers, which only need grass for their youngsters. Silver-washed fritillaries are holding their own if not increasing. They need violets in sunny beech woodland. But their cousins, the pearl-bordered and the dark green fritillaries, show little sign of a come-back.

A few foreigners such as swallowtail, Queen of Spain fritillary and short-tailed blue have been tapping on the doors along the Sussex coast

in the past decade and may well come in to establish as breeders before long if global warming carries on.