Two house mosquitoes are present in the United States: the northern house mosquito and the southern house mosquito. The northern house mosquito was introduced from North Africa and is present across the northern US; the southern house mosquito was introduced from Southeast Asia as is present across the southern US. There is a hybrid zone where these mosquitoes meet and are able to produce viable offspring, indicating they are probably subspecies instead of two separate species.
House mosquitoes can vector the West Nile virus (and other diseases that may cause encephalitis) from birds to humans and horses. They are more likely to vector these diseases in urban areas because of their preference for living and breeding near humans. Since house mosquitoes overwinter as adults, they are often found in structures during cold temperatures. Females may bite when indoor heating or the weather becomes warm enough. Although they will breed anywhere water is allowed to accumulate, they prefer to lay eggs in stagnant water rich in organic matter, as in sewage or drainage systems and in pastures.
Removing standing water on properties reduces house mosquito populations. Otherwise, insect growth regulators (IGRs) labeled for mosquitoes can be applied to standing water in items such as planter saucers, bird baths, and gutters to prevent larvae from developing into adults. Apply liquid residual insecticides to adult mosquito resting sites under shady and secluded areas such as foliage, eaves, and decks. Significant populations of overwintering adults can be treated with liquid residual insecticides to reduce the number of adults that will emerge in the spring.