Lysandra bellargus (Adonis Light Blue)
 
The Adonis blue (Lysandra bellargus, also known as Polyommatus bellargus) is a butterfly in the family Lycaenidae. It is found in the Palearctic ecozone (Western Europe, Central Europe, South Europe, South Russia, Iraq, Iran, Caucasus, Transcaucasus, Turkey).
It may be found in chalk downland, in warm sheltered spots, flying low over vegetation, seeking females that are rich chocolate brown in color. The male has brilliantly-colored wings that give it its name.  The male has the upper side wings a brilliant sky blue, with a fine black line round the edge and a white margin. The female is chocolate brown with a few blue scales near the base, and with orange spots, bordered by blue scales, around the edge of the hind wing. The fringes are chequered both sexes. The underside is brownish grey with black and orange crescent spots. The wingspan is about 3 cm (1.2 in). The caterpillar reaches 1.6 centimetres in length, has a dark green body with dark spines , and yellow bands along the back and sides.  In Britain, the Adonis Blue is at the northern extreme of its range and has always been restricted to the warmer dry calcareous grasslands of southern England. It has suffered a huge decline in the past 200 years, and has been lost from Cambridgeshire, Essex, Suffolk, and the Chilterns. The strongholds are Dorset, Wiltshire, Sussex and the Isle of Wight. Over the whole of Britain there has been a decline of over 90% in numbers of this species since 1950.