Chalkhill Blue, Polyommatus coridon

Polyommatus coridon
Brighton, Photo: Dan Danahar

Recorded sightings in 2009: 0

Recorded sightings in 2010: 3

Status in Rother: As this is mainly a butterfly of Chalk (and Limestone) grasslands, sightings in the Rother Area would be quite rare. In good years male Chalkhill blue populations can become very large in August and the butterfly will then disperse into other areas.

Habitat: Chalkhill Blue is usually found on exposed, south facing slopes of steep downs. It's sole foodplant is Horseshoe Vetch. The re-introduction of grazed downland has been extremely important for this butterfly, as the loss of habitat due to scrub invasion resulted in population decline. Restricted now to mainly the southern counties of England colonies of Chalkhill Blue often need to be safeguarded on well managed Nature Reserves.

Foodplant: Plants other than Horseshoe Vetch are occasionaly used in warmer areas of continental Europe. Some of which occur here in Brittan such as Birds-foot trefoil, Crown vetch and Milk vetch (Tolman, T. 1997, Butterflies of Britain & Europe, Harper Collins).
It is likely that the higher temperatures in southern Europe allow both a wider range of plant species (that the larvae have the correct enzymes to devour successfully) and better digestion of marginally suitable plants. In Britain a colony of Chalkhill Blue survived briefly on Epping Common between 1859 to the mid 1860s, where there is no Horseshoe Vetch, it was found they were using Birdsfoot trefoil as a host plant and it would appear significant that the London to Loughton railway opened in 1856 and the soil disturbance may have helped create suitable habitats and insects may have been accidentally helped to travel along the railways (Corke D. 1997. The Butterflies of Essex. Lopinga Books).
With climatic change or a warmer climate, it could be possible that Chalkhill Blue may be able to use an alternative host plant in years to come, there by, enabling the species to gradually colonise areas off the downs. However, this is speculation as there are probably habitat requirements other than just the food plant to consider but it is still worth keeping an eye on these invaders from the downs it is just possible some could be there next year.

ID Tips: The male Chalkhill Blue is paler and larger than other blue butterflies seen in Rother. The underwing is aslo more grey than brown, and heavily spotted. The female butterfly is brown.

First sighting in Rother (2009): Not recorded
Recorded by: Not recorded

First sighting in Rother (2010): 19 July
Recorded by: Katie Walker

UK Distribution trend: -36%

Ten year UK Population trend (1995-2004): -34%

Long term UK population trend: 31%

Distribution map