1)
The black spot on the forewing is clearly marked. It is not so obvious
in the Common Blue.
2)
The orange lunules on the forewing are clearly marked - not conclusive
in itself. As they aren't strong right to the front of the wing this
is a male Brown Argus.
3)
No obvious white in the orange lunules on the hind wing.
4)
There are clearly marked continuation of the veining into the white fringes
of the wing (like Adonis Blue).
5)
There is no evidence of blue in the wings. The slight bluish tinge in
the hind wing doesn't count. This iridescence is common in the blues and
can be seen in Small Coppers too, depending on how the light catches
them.
6)
Size. Judging from the ragwort flower it looks about the right size. Although
there isn't much in it size wise.
You've snapped this one right at the start of the second brood, so it's in rather good nick. Keep and eye out for more as the second brood should be around for the whole of August.
Cheers
1)
On the underside hind wing of the Brown Argus
two of the spots line up to form a colon ':' (See A on the picture),
whereas on the Common Blue the second spot is in line with the rest of
the spots that follow the shape of the wing (See B on the picture).
2)
If the underside of the forewing is exposed enough, then the Common Blue
has spots closer to the body than the mid-wing elongated spot (See E on
the picture). The Brown Argus
does not have these, but that part of the wing is rarely exposed.
3)
On the upper wing the mid-wing spot is either not visible or not very prominent
in the female Common Blue (See C on the picture).
4)
The female Common Blue has prominent areas of white on the upper wing that
is not present on the Brown Argus
(See D on the picture).
Cheers
Addenda: The orange spots have only been recorded to the front edge of the forewings in Brown Argus. AH