Chalk Hill Blue (Polyommatus coridon)

Species description
© - Nick Greatorex-Davies

The Chalkhill Blue, as its name suggests, is restricted to chalk and limestone grassland where its foodplant Horseshoe Vetch (Hippocrepis comosa) grows. Though still widespread in these habitats it is far less common than it once was because of the destruction of herb-rich calcareous grassland due to agricultural intensification. (For further details on this species see

Trend summary

Status since 1976 is Stable with a change of 1.0% since monitoring began for this species.
Status over the last 20 years is Stable with a change of 18.3%
Status over the last 10 years is Stable with a change of -24.0%

Log Collated

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 April 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.