It is hard to believe that pipiens was once rare in the province. Hearle wrote in 1926 "It would appear that this species has been introduced comparatively recently". It "has been taken, but is very rare, and so far has been found at one point only" (Vancouver). In recent years, it has spread widely and increased enormously in numbers and is now common from Vancouver Island at least to the Okanagan.
On emergence from hibernation fertilized females seek a blood meal and soon lay their eggs in boat-shaped rafts on the surface of water in sewage lagoons, drainage ditches, catch basins, paddling pools, tin cans and also in natural open pools and swamps. The new generation matures, mates and lays its eggs in three to five weeks. Several generations are produced each season, the number depending on the temperature of the breeding site. In the Lower Mainland I have seen groups of about ten males swarming over Douglas Spirea bushes in summer and close to the south walls of buildings later in the season, often until the first killing frost. By then the mated females have found humid places to hibernate, often within buildings.
There has been much debate about the varied behaviour of this species and whether or not there are two strains, only one of which bites humans. In the many ditches of the Richmond area it is often abundant, yet seldom annoying outdoors. On the other hand, it is a pest when it enters houses in late summer and bites the inhabitants. Most residents in the southwest of the Province have experienced its whine around their heads as they tried to sleep. Although the Richmond strain seldom bites outdoors it has been successfully colonized and will feed on guinea pigs in a warm humid laboratory (Gillespie 1978). Specimens naturally infected with SLE and WEE have been found in Washington State (Gjullin & Eddy 1972).