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Large Blue (Maculinea arion)

On this page, we have made available all the information we have for this species

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Picture of Large Blue
© 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

Family : Lycaenidae

Status : Rapid increase

Status details :
Status since 1983 is Rapid increase with a increase of 1306%
Status over the last 20 years is Rapid increase with a increase of 503%
Status over the last 10 years is Stable with a increase of 25%

Log collated index plot

Species Log Collated Index Plot

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). For greater detail about how this index is derived, click on the green question mark above.

Trend description :
This species has significantly increased on monitored sites since its reintroduction in the 1980's. This increase has plateaued with the short-term trend being classed as stable. This is evident at a site level with the majority of monitored sites for which there is sufficient data to calculate long-term trends also showing a stable population. This endangered UK BAP priority species has recently colonised new sites from the cores of its reintroduced populations. The success of this butterfly owes itself to detailed studies on its complex ecology and subsequent appropriate habitat management led by Prof. Jeremy Thomas.

This map shows the distribution between 1995 and 2014. Data is derived from the Butterflies for the New Millenium dataset via the NBN Gateway

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Phenology plot
Species Phenology Plot

Phenology plot

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.

blank abundance map - no data available


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.


In total, Large Blue has been recorded from 3 transects in the Butterfly Monitoring Scheme. Of these, annual indices of abundance have been calculated from 3 sites, with an average index of 0 individuals per site.

For 0 of these sites, Large Blue has been recorded well enough to calculate annual indices of abundance in more years, allowing trends to be calculated.

In 2015, 14 individuals were recorded from 3 sites, producing annual indices at 2 of these.

The UKBMS is run by  Butterfly Conservation (BC), the Centre for Ecology and Hydrology (CEH) and the British Trust for Ornithology (BTO), in partnership with the Joint Nature Conservation Committee (JNCC), and supported and steered by Forestry Commission (FC),  Natural England (NE), Natural Resources Wales (NRW), Northern Ireland Environment Agency (NIEA), and Scottish Natural Heritage (SNH). The UKBMS is indebted to all volunteers who contribute data to the scheme.