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Interesting ... I wonder if these are Philygria (=Nostima) picta - in this species both sexes have reduced wings, but the reduction is more extreme in the female (- sexual dimorphism rather than polymorphism). Among the Philygria that David suggests, semialata was originally placed in Nostima, distingished by plumose arista and two, rather than three, dorsocentral pairs (including pre-scutellars). It is a species that is most often recorded by pitfall trapping, in Britain associated with grassy heaths.
If you have found a different Philygria with fully macropterous and brachypterous forms, then that is certainly remarkable! In any case a good find! B)