THE following circumstance may prove interesting, and probably new, to some of your entomological readers. On September 10, in a gathering of pond-water made in this neighbourhood and brought home for microscopical examination, a somewhat singular and unusual object presented itself, but speedily making its way to the sediment at the bottom, it became lost to fight. Upon the evening of the 12th, or after the lapse of fully two days, while holding the bottle to the light, the same object again appeared, swimming or flying in mid-water with a peculiar jerky movement resembling that of some of the Entomostraca, and for one of which I at first mistook it. On removal by means of a dipping-tube to a zoophyte trough for fuller examination, it proved, to my great surprise, to be one of the small Hymenopterous flies of the Proctotrupid family, and here it continued its active movements, now walking and running upon the bottom and sides of the trough, now flying, as it were, through mid-water by the energetic movements of its wings, but apparently making no effort to escape. Examination thus proving no easy task while living, and fearing the loss of a specimen of habits so unique, I decided upon securing it permanently as a microscopic mount. With a minute description I need not now trouble you, but as neither in Westwood nor in any other of the authorities on such subjects at my command I can find any record of this singular fact having been hitherto observed, either in connection with the parasitic Hymenoptera or any other similar insects in the perfect state adapted apparently to an aerial life alone—that they should quit their natural habitat for so lengthened a sojourn in the water—I would make the inquiry as to whether any like occurrence has been noted by any of your other correspondents.