The Chalk Hill Blue butterfly Polyommatus coridon is Britain's most variable butterfly. The normal underside wing spotting can be reduced or missing, or very rarely the spots may form streakes. The topside wings can also vary in colour, but extreme variation is rare. A selection of  type and different aberrant forms that I have photographed is shown below. 



The above picture of male Chalk Hill blues nectaring on Carline Thistle has been published many times, and the photo was taken at Houghton Regis quarry.


Above a male ab. fowleri with white squares replacing the dark fore and hindwing bands. This form is fairly rare, but occurs frequently (perhaps one in a thousand) in some colonies. A simple recessive gene is responsible and is easy to breed. The above butterfly was photographed in August 2010 in a small Bedfordshire coloney where I had not seen it before.


The females are typically brown on the top wing surface.


Above a very rare colour form of the female ab. khaki.


This ab.tithonus (formally named syngraphy) is the all blue form of the female and is very rare in Britain.


Females with some blue on their wings are uncommon but do occur in some colonies. This one is approaching ab. semi-syngraphy.


Mating Chalk Hill blues ahowing the typical underside spotting of male (top) and a female.


A rare ab. radiata form of the male.


Above the ab.ceaca form has all the underside spots missing, and is not as rare as the streaked forms, but still uncommon in most colonies.


All pictures are Copyright of Richard Revels FRPS