Mosquitoes are a common concern in Southern California due to their potential for transmitting diseases. Understanding the typical “mosquito season” helps residents prepare for periods of increased mosquito activity, when populations are most active and abundant.
Understanding the Mosquito Calendar
Mosquito season in Southern California generally extends from late spring through early fall, often peaking in July and August. Some sources indicate the season can run from March to late November. Warmer temperatures during these months create favorable conditions for mosquito breeding and development. While there is a typical season, mosquitoes can remain present year-round in varying numbers due to Southern California’s mild climate. Invasive Aedes mosquitoes, known for their aggressive daytime biting, can also survive throughout the year in urban settings.
Key Influences on Mosquito Activity
Several environmental and climatic factors determine mosquito activity in Southern California. Temperature plays a significant role, as mosquitoes become active around 50 degrees Fahrenheit and thrive above 70 degrees Fahrenheit. Warmer temperatures accelerate mosquito metabolism and breeding cycles, leading to faster development from egg to adult, sometimes in as little as seven days.
Rainfall patterns also heavily influence mosquito populations. Mosquitoes require stagnant water to lay eggs, and increased rainfall creates more breeding sites in puddles, clogged drains, gutters, and small containers like flowerpot saucers. Heavy rains can lead to a rapid increase in mosquito populations, as eggs can hatch within 24 to 48 hours in standing water. However, excessive rain can also flush out some breeding grounds, temporarily reducing populations. Humidity further supports mosquito survival and reproduction, contributing to higher activity in moist, warm environments.
Public Health Concerns During Mosquito Season
Increased mosquito activity during Southern California’s warmer months brings public health concerns related to mosquito-borne illnesses. West Nile virus (WNV) is the most common mosquito-borne disease affecting residents in California. Mosquitoes become infected with WNV by feeding on infected birds, then transmit the virus to humans through bites. Most people infected with WNV do not develop symptoms, but some may experience fever, headache, body aches, joint pains, vomiting, diarrhea, or rash. Severe cases can lead to neurological damage.
Invasive Aedes mosquitoes (Aedes aegypti and Aedes albopictus) are also present in Southern California and can transmit viruses like dengue, Zika, chikungunya, and yellow fever. While most dengue and Zika cases in California have historically been travel-related, instances of locally acquired dengue have occurred. Local transmission of Zika in California has been very rare, with most cases linked to travel or sexual contact with infected travelers.