Mosquitoes are present in Colorado, often surprising visitors due to the state’s arid reputation. Their presence varies across diverse landscapes, influenced by water availability and seasonal weather patterns. Understanding where and when these insects are most active, along with health considerations, can help residents navigate the warmer months.
Where and When They Are Found
Mosquito activity in Colorado is closely tied to standing water, which serves as a breeding ground. Sources include irrigation runoff, melting snow, and accumulated rainwater. Elevated precipitation often leads to increased mosquito populations. Mosquitoes lay eggs in small amounts of standing water, such as clogged gutters, bird baths, or old tires.
The mosquito season in Colorado typically spans from late spring through early fall, generally from April or May until the first hard frost, which can be in September or October. Activity is highest during the summer months, particularly from July through September. While mosquitoes can be found at nearly every elevation, their activity and abundance vary depending on local climate and habitat conditions.
Species and Health Concerns
Colorado is home to over 45 different mosquito species. Two common groups are the Aedes and Culex genera. Aedes mosquitoes, often called floodwater mosquitoes, bite during the day, especially near standing water from rain or snowmelt. Culex mosquitoes, including Culex tarsalis and Culex pipiens, are typically more active around dawn and dusk.
Not all mosquito species transmit diseases, but some carry pathogens. West Nile Virus (WNV) is the primary concern in Colorado. Mosquitoes become infected with WNV from birds, then transmit it to humans through bites. Most infected people (about 80%) do not develop symptoms; for those who do, symptoms are flu-like (fever, headache, body aches), appearing 2 to 14 days after exposure.
A small percentage, especially those over 50 or with certain medical conditions, can develop severe neurological illnesses like encephalitis or meningitis. Colorado has reported WNV cases annually since 2002, with a significant outbreak in 2023.
Prevention and Control
Protecting oneself from mosquitoes in Colorado involves personal actions and managing one’s surroundings. Using EPA-registered insect repellents is a recommended personal protective measure. Wearing long-sleeved shirts and long pants, especially during peak mosquito activity times like dusk and dawn, also reduces exposure to bites.
Managing potential breeding sites around the home is an effective way to reduce mosquito populations. This includes regularly draining standing water from common outdoor items such as bird baths, flowerpots, old tires, and clogged gutters. Ensuring window and door screens are in good repair also helps prevent mosquitoes from entering indoor spaces. Communities across Colorado also implement mosquito management programs that involve monitoring mosquito populations, treating larval habitats, and conducting public awareness campaigns.