Mosquitoes are present in Denver, Colorado. Understanding their activity and potential health concerns helps residents take effective measures to reduce exposure.
Mosquito Presence and Seasonality in Denver
Mosquito activity in Denver typically begins in late spring, around May, and continues through early fall. Populations are highest during summer, concluding after the first hard freeze. Mosquitoes thrive in temperatures between 50 and 95 degrees Fahrenheit, with populations influenced by rainfall and temperature.
Despite Denver’s dry climate, irrigation, rivers, and storm runoff create numerous breeding sites. Even small amounts of standing water can serve as nurseries for mosquito larvae. Common outdoor locations that collect water, including gutters, birdbaths, old tires, buckets, flowerpots, and children’s toys, become ideal breeding grounds. Wet springs and hot summers can lead to increased mosquito populations.
Health Risks and Key Mosquito Species
The primary health concern associated with mosquitoes in Denver is West Nile Virus (WNV). This virus is transmitted to humans through the bite of an infected mosquito, which acquires the virus by feeding on infected birds. WNV has been endemic to Colorado since 2002.
Most individuals infected with WNV do not experience symptoms. About one in five may develop mild symptoms, including fever, headache, body aches, joint pain, vomiting, diarrhea, or a rash. A small percentage may develop severe neurological illness, characterized by high fever, severe headache, neck stiffness, disorientation, tremors, seizures, paralysis, or coma. The primary mosquito species transmitting WNV in the region are Culex pipiens and Culex tarsalis. Other mosquito-borne diseases like Zika or Dengue are generally not transmitted within Denver.
Community and Personal Mosquito Management
Public health agencies in Denver actively monitor mosquito populations to mitigate risks. Their programs focus on reducing breeding sites and controlling larval populations through surveillance and larvicide application. Surveillance also includes trapping adult mosquitoes for testing to detect West Nile Virus.
Individuals can take practical steps to reduce mosquito exposure around their homes. Eliminating standing water is highly effective, as mosquitoes require water for their life cycle. This involves regularly emptying and scrubbing items that collect water, such as tires, buckets, planters, birdbaths, and trash containers. Clean, free-flowing rain gutters also prevent water accumulation.
Personal protection measures include using EPA-registered insect repellents containing active ingredients like DEET, picaridin, IR3535, or oil of lemon eucalyptus when outdoors. Wearing long-sleeved shirts and pants, especially during dawn and dusk when mosquitoes are most active, can also help prevent bites. Maintaining intact screens on windows and doors helps keep mosquitoes from entering homes. Keeping lawns trimmed and removing dense vegetation can reduce resting spots for mosquitoes during the day.