White Ermine (Spilosoma lubricipeda) distribution and trends

in Berkshire:

VC22 Berkshire map based on data held by Martin C. Harvey on the MapMate database

Trends

According to The state of Britain's larger moths, White Ermine suffered a national decline of 77% from 1968 to 2002. Our Berkshire data (which is a much less statistically valid dataset) doesn't show a clear local decline, and could be interpreted as having a ten-year cyclic pattern (but we don't have a long enough run of data to prove this):

Jan Haseler recently reported what was only the second record of White Ermine in her well-recorded garden. For comparison, I looked at all Berkshire sites that have had at least 100 moth records since 1990 during the White Ermine's flight period (April to July). Of the 88 sites that fall into this category, 68 have recorded White Ermine at least once.

Without doing any statistical analysis, the data appears to show a fairly clear correlation between total number of records and the number of White Ermine records - for instance, the top five most well-recorded sites were also the top five sites for numbers of White Ermine records, and most of the sites with no White Ermine records were near the the bottom of the table as far as total number of moth records was concerned.

On average, at any given site White Ermines make up 0.8% of all the moth records from April-July, i.e. you are likely to record a White Ermine once in every 125 moths you record.

So, Shirley Spencer's former house in Riseley was a White Ermine haven, with over five times the expected rate (and this site is the only one in Berks that has such a positive anomaly for White Ermine). And Jan's garden has been a White Ermine desert, the proportion of White Ermines being lower than at any other site that has recorded the species at all. But it is perhaps improving - before this year she was seeing White Ermines at only a tenth of the expected rate in Berkshire, but her 2009 sighting means she has now moved up to a fifth of the average!

I can't see any obvious correlation between frequency of White Ermine and type of habitat, and it seems equally at home in urban areas and in the countryside.