Metamorphosis of an adult northern house mosquito Culex pipiens, from its pupal form on the surface of water. Mosquito larvae hatch on the water suface from clumps of eggs laid in the spring; although heavier than water, the larvae are able to remain suspended from surface through surface tension effects on a ring of hairs that surrounds the opening to the trachea (airway). Pupation occurs after 4 larval molts over a three week period. The imago (young adult) emerges after a few days, with its pupal case acting as a buoyancy platform before splitting. Third in sequence of 4 photos.