Mosquitoes are more than a nuisance. They can carry West Nile virus (WNV). Boulder County Public Health works to prevent the transmission of WNV in Boulder County and to address nuisance mosquitoes.
There is no treatment for West Nile virus, so it’s important to prevent it. West Nile can cause a debilitating illness in 20% of those infected. Everyone should protect themselves against mosquito bites.
Follow the 4Ds when mosquitoes are most active (June through September).
Use insect repellent that contains at least 10% DEET. If outside during evening, nighttime, and dawn hours, consider using an insect repellent containing 10% to 30% DEET (N, N-diethyl—methyl-meta-toluamide). Products with concentrations around 10% are effective for approximately two hours.
Use DEET according to the manufacturer’s directions:
Find the Repellent that is Right for You
Dress in long sleeves and long pants. Children and adults should wear protective clothing such as long pants, long-sleeved shirts, and socks if outside during evening, nighttime, and dawn hours when mosquitoes are most active and likely to bite.
Reduce or eliminate outdoor activity between dusk and dawn.
Make sure windows are closed or screened.
Most mosquito species actively search for a blood meal in the evening from just before dark until 2 to 3 hours after dark. During the daytime, females normally rest in cooler vegetated areas where the humidity is higher, and they are protected from drying out. Females will often bite in the daytime if humans or animals invade the wooded areas where they are resting.
Make sure to drain standing water around your home.
Adult mosquitoes are most active at dawn and for about an hour after dusk. Plan outdoor activities during warmer daylight hours or later in the evening to avoid adult-biting mosquitoes.
Residents dealing with mosquito issues in various cities can report problems to these contacts.
Boulder County Public Health (BCPH) monitors mosquito populations, especially the Culex species, to determine the risk to people.
BCPH has traps throughout Boulder County so that we can count
The Culex mosquito is a carrier of West Nile virus in Colorado. It is common in Boulder County and takes about two weeks to grow in warm weather. Getting rid of standing water can help stop them from multiplying.
Learn more about Culex mosquitoes (CDC)
BCPH looks at mosquitoes captured in traps throughout Boulder County and tracks the data for trends.
Total Culex: Weekly Comparison by Year
Vector IndexThe vector index, which measures the risk of the virus spreading, depends on the number of Culex pipien and Culex tarsalis mosquitoes trapped and tested. If the vector index reaches 0.75 or more, there might be a need to take action to reduce the number of mosquitoes in Boulder County. We do this by using:
| n/a | Zone 1 | Zone 2 | Zone 3 |
| Week Ending On | Vector Index | Vector Index | Vector Index |
| June 29 (Week 25) | 0.00 | 0.00 | 0.00 |
| July 6 (Week 26) | 0.00 | 0.00 | 0.00 |
| July 13 (Week 27) | 0.00 | 0.00 | 0.00 |
| July 20 (Week 28) | 0.00 | 0.00 | 0.00 |
| July 27 (Week 29) | 0.00 | 0.36 | 0.00 |
| August 3 (Week 30) | 0.00 | 0.00 | 0.00 |
| August 10 (Week 31) | 1.33 | 0.42 | 0.00 |
| August 17 (Week 32) | 0.24 | 1.35 | .54 |
| August 24 (Week 33) | 0.00 | 0.23 | 0.00 |
| August 31 (Week 34) | 0.20 | 0.45 | 0.19 |
| September 5 (Week 35) | 0.20 | 0.00 | 0.14 |
| September 7 (Week 36) | — | — | — |
A comprehensive mosquito management strategy is employed to address the dual challenge of nuisance and potential health risks posed by mosquitoes as carriers of the West Nile virus. The approach is anchored in Integrated Pest Management (IPM), a method designed to reduce mosquito populations effectively while prioritizing environmental friendliness and cost-effectiveness.
This approach focuses on preventing breeding by
The Boulder County Mosquito Control District (BCMCD) works to keep residents safe from mosquito-related health issues. Meetings, either virtual or by phone, help everyone stay connected and informed. Annual reports give a peek into ongoing mosquito control efforts.
The Boulder County Mosquito Control District (BCMCD) was established in 1995 by ordinance by the Board of County Commissioners to protect residents from the health risks, annoyance, and discomfort associated with mosquitoes.
The second Wednesday of the month
April – October
6 – 7:30 p.m.
The Boulder County Mosquito Control District surveyed residents in 2011 to gather feedback on mosquito control practices. The responses overwhelmingly indicated that people want mosquito control to continue. Many stated that mosquitoes negatively impacted their ability to enjoy the outdoors.
The Boulder County Mosquito District encompasses approximately 180 square miles of eastern Boulder County. Because the residents who live within this district pay for mosquito control services, Boulder County can only provide mosquito control services to those who live within the district.
Printable Map of Boulder County Mosquito Control District
The Boulder County Mosquito Control District (BCMCD) Program is overseen by a citizens’ advisory board appointed by the Boulder County Commissioners.
Services that are available, upon request, to those living within the Boulder County Mosquito Control District include:
The board promotes an integrated pest management program, collaborates with agencies to control mosquito-borne diseases, educates residents in the BCMCD to help identify and reduce mosquito breeding sites around their homes and neighborhoods, and advises the County Commissioners and Boulder County Public Health on mosquito control activities and needs.
The Boulder County Mosquito Control Program (BCMCP) is one of the most environmentally conscious programs in the nation. Mosquito control services in Boulder County are contracted to a company, Vector Disease Control International (VDCI).
VDCI utilizes an integrated pest management approach to safely and effectively reduce mosquito populations. The National Cancer Institute has shown that all mosquito control materials used in Boulder County are non-carcinogenic and are registered for use by the Environmental Protection Agency (EPA).
West Nile virus (WNV) poses a significant health concern in Colorado. Approximately 20% of those infected may experience severe symptoms, ranging from fever and fatigue to more serious conditions like meningitis or paralysis.
These guidelines are provided to assist health care providers and educators with the recognition and diagnosis of illness due to West Nile virus (WNV).
Please feel free to download, reproduce, and distribute these materials.
The One Bite campaign was developed in 2003 when Boulder County had an extreme number of people who contracted West Nile virus. A significant number of residents died or had long-term or permanent complications.
