White-letter Hairstreak (Satyrium w-album)
© - Eddie John
The White-letter Hairstreak is a very elusive butterfly that spends most of its time high up in the canopy of Elms (Ulmus spp.), on which it breeds, in woodlands and hedgerows. The butterfly is still widespread but far less common than it was before the ravages of Dutch Elm Disease. (For further details on this species see http://www.butterfly-conservation.org/).
Status since 1976 is Rapid decline with a change of -78.0% since monitoring began for this species.
Status over the last 20 years is Stable with a change of 21.2%
Status over the last 10 years is Rapid increase with a change of 197.0%
This chart shows the index of abundance (LCI = Log Collated Index) over time. It shows fluctuations in populations from year to year, and is scaled so that the average index over the whole series is equal to 2 (horizontal line). Further details on the analysis of UKBMS data can be found [here]
This chart shows the average number of butterflies seen on transects between Arpil and October across all sites (fitted values from a Generalised Additive Model). The blue line gives average counts over the full BMS series (1976 to date) and the red line gives the average for the last year.
This map shows symbols for the mean abundance at transect sites, with the colour of the symbol reflecting the level of abundance. Means are over all years. Grey background squares are the occupied cells as shown by the Butterflies for the New Millenium over the previous ten year period.