Blog post Theresa Shelton

Rainy Weather and Mosquitoes

Do wet or dry years create more mosquito problems?  One might immediately assume wet years because mosquitoes need water to breed.  On the other hand, droughts create pools and puddles in water bodies like rivers and streams that would otherwise be flowing too strongly for mosquitoes to utilize.  The reality is both weather patterns cause different types of mosquito control challenges.

Drought years are associated with higher rates of West Nile Virus. The probable reasons for this include higher temperatures which promote virus replication, reduced water flow, and high concentrations of birds gathering at limited water sources which increases bird-to-bird transmission as well as makes it easier for mosquitoes to find a meal. Even during a dry year, there are many sources of water that may promote mosquito breeding. Overwatering may support mosquito species in back yard and underground sources unless residents make efforts to reduce water consumption.  Water conservation efforts, such as containers for rain water storage, may also support breeding mosquitoes if they are not carefully covered or monitored.  Finally, some catch basins will also hold standing water that breeds mosquitoes until a rain storm flushes it out.

Rainy years certainly promote mosquito breeding, particularly for species that breed in marshes and fresh water natural sources. Water collects in low lying areas called “impounds” that create favorable habitat for many bay area mosquito species. Some marsh areas that are normally dry can contain dormant eggs of some mosquitoes that will last for years until a rainy year causes the water to rise over them, triggering hatching.  Additionally, urban mosquito species also benefit from the variety of buckets, containers, and items that fill with rain water in residents’ yards.  Inspecting and treating these sources takes a lot of time and hard work.