the females lay a vast number of eggs on grass stems near water. when the larvae are born they drop into the water or the ground nearby it and make their way into their new aquatic biome. the larvae are aquatic, active, armed with strong sharp mandibles, and breathe by means of seven pairs of abdominal branchial filaments. when full sized, which takes between one and two years, they leave the water and spend a quiescent pupal stage on the land before metamorphosis into the sexually mature insect. adult alderflies stay near to the water in which they had lived when they were younger. once in their adult stage, they tend to live only 2 to 3 weeks, which they spend mainly in reproducing.