As it turns out, severe drought has a silver lining.
For the first time since 2013, the City of Longmont did not conduct any mosquito spraying operations this year. Although drought and low rainfall are causing major problems elsewhere, it’s also believed to have taken a toll on mosquito populations.
Cause and infect
Per the City of Longmont website, spraying is used to control the spread of West Nile Virus. But triggering it must satisfy two conditions: Traps in a neighborhood must exceed 150 mosquitoes and West Nile Virus must be discovered in Larimer, Boulder, or Weld Counties.
WNV human infections were detected eight times between the three counties (including one in a Longmont resident), but mosquito abundance has been below the five-year average for most of the season, according to Jim Krick, the City of Longmont’s ecosystem manager.
Krick added that while it’s difficult to pinpoint an exact cause, it’s thought that mosquito activity is being slowed by the lack of rain, reductions in residential, commercial, and municipal watering, as well as diminished agricultural irrigation. Since mosquitoes breed in pools of water, those factors tend to attract mosquitoes like college frat boys to a happy hour.
Look on the bite side…
Although our region is severely parched, it appears to have caused a significant reduction in mosquito presence and, therefore, WNV infections. That’s welcome news for anyone — but especially for residents in Boulder, Weld, and Larimer counties. Those three counties represent the biggest hot spots for WNV human infections in all of Colorado.
Since reporting began in 2003, Boulder County has recorded 913 WNV cases — the third most of all Colorado counties, according to the Colorado Department of Health. 2025 clocked 38 cases. This year, there have only been four.
Larimer County has tallied the most infections all-time for Colorado counties, with 1,122.
Krick said that a Colorado State University study linked the large amount of irrigated agricultural land in the three counties to the prevalence of infections.
Zooming out:
Despite reduced mosquito activity, Krick advises caution as WNV is still being detected. He encourages residents to protect themselves by using insect repellent, wearing long sleeves and pants while outdoors, avoid being outside during dusk until sunrise (peak mosquito activity timeframe), and drain standing water.