Non-biting mides (Chironimidae) by nightfly at 1:02 am 30/10/12

Confidence: It's likely to be this, but I can't be certain.

Notes: They aren't right for caenis, much more like the elongated narrow abdomens of Chironimidae, the exuviae left behind by the hatching flies. The thoracic part of the exuviae is visible as a dark thing at one end of the clear segmented abdominal part, thats where the insect emerged from. The dark bit is the opening from where the fly escaped its pupal exuviae, you can actually see inside the empty thoracic portion which is exposed to the air. Caenis nymphal exuviae(not pupa) are much more squat/short and broad in proportion to their length. With caenis you can't see the hole where the fly emerged from as easily as in Chironimidae.