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Sighted at Brook Down Quarry, Isle of Wight, on May 19th 2016.
I thought they were Adonis blue but think they are actually common - any ID hints?
Thanks

These are all Adonis.

There are lots of reasons for this, some more subtle than others. The group of blues that Adonis belongs to (Lysandra) have prominent androconial furriness in the forewings that common blues lack. All these show this clearly [EDIT: the middle picture shows this clearly - the others indirectly], so cannot be common blues. The fringes are also a good sign. Common blue may show chequering in the inner half of the fringe, which is darker in tone than the outer, but all these show dark marks extending into the outer half of the fringe - and the inner half is not darker.

These are the obvious signs. There are other more subtle signs that come with experience of both butterflies.

Guy

Many thanks for the ID help - very interesting, more detail than in my guide book - and a new butterfly for me.
Thanks again