Large Blue (Phengaris arion)

Species description
© - Eddie John

In Britain the Large Blue is a rare and highly localised butterfly of very short herb-rich grassland where its foodplant Thyme (Thymus spp.) grows in the presence of its host ant, Myrmica sabuleti, in whose nests it spends its later larval and pupal stages. After becoming extinct in Britain in 1979, it has been successfully reintroduced to a number of sites in the south-west of England. (For further details on this species see

LCI summary

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.