Keys out to Oecothea using the MND heleomyzid key (1) (MND uses the junior synonym Aecothea). If I’ve got the genus correct, the descriptions in Gill’s 1962 paper (2) rule out O. aristata because the scutellum has setae and the unclouded wings rule out O. fidelis (plus the fact that Maryland is nowhere near Siberia). That leaves O. specus and O. fenestralis which Gill says can only be distinguished by the male terminalia.

I’d appreciate confirmation/correction of the genus ID. TIA