The Dark Green Fritillary has one brood per year, over-wintering as a caterpillar. The adults fly from late June to late August.
The food plants are various species of violets, depending on which are available in the locality.
The nearest I have seen were at Fleam Dyke in Cambridgeshire. On a bright day they disappear after about the first hour that it it is warm enough for them to fly.
The cloud did not lift until about 9.30 on 26 June 2011, and the butterflies disappeared at about 10.30 am.
27 June 2011 started hot and clear and none were seen in the morning after 9.30 am.
Their flight is not very high, but swift and purposeful. Their nectaring visits are so brief that I took the first photographs by sitting by a prominent thistle and waiting for the butterflies, later that morning I found a windless spot at the bottom of the dyke where I could stand by a tall clump of thistles which was being continually visited, once with three at a time.
The photograph of 23 July 2011 shows how the colour fades as they get older.