Here is a female Culex pipiens that I just found in my mother's house. It has the hypertrophied fat body typical of overwintering females. Almost looks like it is gravid, but dissection would reveal the ovaries in Christopher's stage II only. They are inseminated, and when they emerge from hibernacula, they seek a bloodmeal to mature their eggs. In colder climates, Anopheles, Culiseta and Culex all undergo this "reproductive diapause". Most Aedes s.l., and Psorophora overwinter as eggs, and Coquilletidia and Wyeomyia smithii overwinter as larvae.