Fen Square-spot Diarsia florida
Wingspan c.34 mm.
A very difficult species to distinguish from Small Square-spot Diarsia rubi, and possibly an ecotype of that species.
In general, Fen Square-spot is larger, paler and where both occur together, tends to be single-brooded, flying in June and July, where Small Square-spot has two generations. It also flies later in the night.
As indicated by the vernacular name, its favoured habitats tend to be fens and marshy places. It occurs in a number of places in East Anglia, Cambridgeshire and Yorkshire, and doubtless other areas as well.