The dark green fritillary is not green, it is orange and brown like many of the other fritillary butterflies. The name is not a total falsehood though as if you look closely at one whilst nectaring with its wings closed you will see the underside of the wing is partially green; whether that is dark green is open to debate! In flight it may seem, at first, difficult to tell the dark green fritillary from the superficially similar silver-washed fritillary.
However there two fundamental differences with nothing to do with colouration that will help point you in the right direction. Firstly, the dark green is a butterfly that is rarely seen away from flower-rich chalk or limestone grassland whereas the silver-washed is much more of a woodland species. Secondly, the dark green is a powerful; flyer and flies with a flap. flap. glide, flap, flap, glide ... I do not think I have ever seen that in any other butterfly.
Sadly, there are only eleven reports of dark green fritillary in the Nature of Dorset database for 2017 and 2018 combined which is not a lot to work with however it does show that the this species emerges around week 22 in mid June and can be seen until week week 30, possibly on to week 32, in mid of August, that seem to tie in with what the textbooks indicate.
There are records from thirteen sites in Dorset and every one is fundamentally calcareous grassland; various points along the Purbeck coast seems to be the best places to see them but they are not particularly common anywhere. I find it surprising that there are no reports from Portland as yet.
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