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John - when preparing the genitalia of this female, you need to mount the last few segments of the abdomen dorso-ventrally (not laterally). They need to be cleared, either beforehand (in KOH or lactic acid), or while it is mounted (in Berlese medium or similar mountant). The differences between the females are very subtle, so the preparation is critical. The remainder of the abdomen should also be mounted dorso-ventrally, and the head, wings and at least one set of legs should also be mounted separately. If your balcony light is still attracting these flies, it would be good to catch a couple of males - they are usually easier to identify! :)