7th August 2023 - early this month, there was a profusion of various 'blue' butterflies along the Old Railway Cutting, so Andy M decided to take some close-up photos to help identify the various species, and any differences between the sexes for each species.
The three species of 'blue' which are found along the railway cutting are: Holly Blue, Common Blue and Brown Argus. Although Chalk Hill Blue are found relatively nearby along Fleam Dyke, and Small Blue have been seen very occasionally along the Roman Road, neither have been seen along the Old Railway Cutting.
Holly Blue are (slightly) larger than the other 'blues'. They almost always close their wings when resting, and the underside is plain pale blue with a number of small black spots. When flying, their brighter blue upper side can be glimpsed, but the general paleness can help in recognising it. The underside is the same in both sexes.
Holly Blue - pale underwings, with small black spots. Wings mostly closed when resting
Common Blue - the male lives up to the name, and has a striking blue upperside to the wings, darkening towards the body, with black line surrounding, and plain white fringes to the wings. The upperside of the female Common Blue is actually brown with a row of orange spots along the outside edges of each wing - just like a Brown Argus, and therefore in itself is unhelpful in identification. However, both male and female Common Blue have a similar underwing pattern, which has a characteristic 'cell spot' nearest the body on the forewing (see arrow in photo). This cell spot is absent in the Brown Argus.
Male Common Blue - obvious bright blue upper, with black margin and plain white fringe
male Common Blue
Common Blue (male, but both sexes are similar)
Common Blue underside, showing the characteristic 'cell spot'
Brown Argus - similar in size to the Common Blue, both male and female Brown Argus have dark brown upper wings, with a row of orange dots near the edge of each wing, and a white fringe. In the female, the orange dots are brighter in colour and extend right up to the wing tip, whereas in the male the orange dots fade to become absent at the wing tip. One the underside, again both sexes are similar. The 'cell spot' is absent, but on the underside of the hindwing there are two closely spaced black and white spots (so called 'twin spots'), which are much further apart in the Common Blue (see arrows)
Brown Argus pair - male (lower) with orange spots that fade at the tip,
and female (above) with stronger orange spots right to the tip
Brown Argus pair - the same individuals, but with the female showing the underside
Brown Argus (male, but sexes similar).
Note the absence of the 'cell spot' (left arrow), and the two closely-spaced 'twin spots' (right arrow)
Brown Argus pair - male (left) and female (right)
Brown Argus male
Brown Argus - showing absence of 'cell spot' and presence of 'twin spots'
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