The Culex pipiens (left) is the primary mosquito that can transmit West Nile virus to humans, birds and other animals. It is produced in stagnant water. At right is an Aedes vexans, primarily a nuisance mosquito produced from freshwater that it is not a key transmitter of disease. (Associated Press)

The Culex pipiens (left) is the primary mosquito that can transmit West Nile virus to humans, birds and other animals. It is produced in stagnant water. At right is an Aedes vexans, primarily a nuisance mosquito produced from freshwater that it is not a key transmitter of disease. (Associated Press)