Summary Observations are presented on the behavior of A. culicifacies imagines in swarming, mating, and ovipositing in a large outdoor insectary. A. culicifacies imagines swarmed in the evenings when light intensity fell below 2.0 foot candles, the swarms consisting mainly of males. Females entered the swarms and copulating pairs flew away from it. Copulation had a duration up to 15 seconds. It appeared that two essentials for mating were exact light conditions and a sufficient space for flying. The females that mated had usually taken a blood meal. Egg development started before copulation. Noise did not disturb swarming and mating, but white objects and light invariably upset the swarms. There was no special relationship to meteorological conditions, except that during, or immediately after, or before rain, swarming did not take place. Phases of the moon had no effect. Gravid females deposited eggs on the water surface while on the wing and while performing a “hovering” dance above the water surface. They did not rest on the water surface, on floatage, or on the bank edge during this act. Direct light from a flashlight invariably repelled these dancing females so that they flew away. Egg laying took place mainly a little after sunset, when it had become quite dark. But A. culicifacies was found to lay eggs at all periods of the night. Owing to its suitability for these normal functions, our large insectary cage made it possible for A. culicifacies to colonize, and several natural broods hatched out. The colony, however, was not vigorous, which was explained as probably due to the balance between heavy natural mortality of imagines and the relatively small output from the few breeding places provided inside the insectary. Rapid development of ova in the ovaries was noticed and egg laying took place in a few cases between 48 and 72 hours after the first blood meal.