Baetis Niger, muctisor Iron Blue Duns are very widespread of rivers and streams with medium and fast flowing water. The Baetis Pumilus can hatch any time from April to November but are most prevelant in April and May.Emergence of the adults is thought to occur at the surface of the water during daylight hours. The males of this species can be found swarming throughout the day, and often swarming continues until dusk. Once mated, the female Iron Blue fly either pulls herself under the water surface to lay her 1200 eggs directly on a partly submerged stone. In some cases the female Iron Blue fly to the river, where she descends to the surface of the water and releases her eggs in several batches by dipping the tip of her abdomen onto the water surface.