RICHARD WILLIAMSON: Good butterfly season anticipated

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This week 2,000 volunteer butterfly recorders like myself start another season of work.This will be my 42nd year making weekly counts of butterflies at Kingley Vale national nature reserve.

I started the work in 1976 and this research gives an accurate picture of what is happening to our butterflies here in the south. I am hoping to see a few of the butterflies as shown in my picture to start the season. This is a male Orange-tip butterfly looking for a drink on a Cowslip. It will come out a few days before the female. She has black-tipped wings, so you can easily tell the sexes apart. These are fairly common insects in broad-leaved Sussex woodlands and they lay their eggs on Cuckoo-flower, also called Lady’s smock (Cardimine pratensis). Eggs might also be laid on Garlic- and Hedge- mustards.

I am expecting a fairly good butterfly season to come if my past records are anything to go by. Peak numbers happen about every seven years and remain good for three years and then drop down into a trough for four years or so. When plotted on paper it looks like a hospital heart graph. About 30 species make up this graph. Nation-wide we get the same result, more or less.

Many mammal, bird, and insect population swing high and then low in this way, the most obvious being the build-up of Lemmings in the Arctic which cause mass migration and subsequent crash. All of this research into population highs and lows is still in its infancy though. Some butterflies such as members of the Fritillary family seem to be on a very long swing. They swarmed in the 1970s at Kingley Vale and are now extinct there and are almost so in Sussex in general. When will they come back again?

Past records going back to 1830 appear to show that the Comma butterfly is on a very long swing, the peaks being about 100 years apart with declines in between making this insect appear almost extinct. The best places to see butterflies in Sussex are on open downland or deciduous woods with glades. Kingley Vale has both. I expect to see 26 species on my count this year as usual, the highest being 32 species in 1976 and again in 1996.

Most species can be relied on to appear on almost the same date each year. But one worrying trend is for the peaks to be getting lower as time goes by. I walk exactly the same route of four miles each week and at the same time and speed in order to make the counts comparable year on year. Only those butterflies within three metres on either side are counted. The best year was 1991 with nearly 12,000 logged; the worst was in 2001 with only 2,400.

Only this accurate research can tell us what is happening to the planet; it is no use relying on subjective memory or opinion.