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Mosquito Population Surges As Colorado Sees Wetter Weather

It’s no secret that Colorado saw an abundance of rain this summer, with Denver experiencing its wettest June on record. The extra moisture has done an impressive job of transforming the Front Range scenery from its usual semi-arid climate into a lush green landscape. Along with the rain, also come mosquitos.

If you feel like you’ve been getting more mosquito bites this year than in the past, you’re probably right. Dr. Bob Hancock, an entomologist from Metropolitan State University of Denver, said there are, without a doubt, more mosquitos buzzing around and he has evidence to back it up. 

“I looked at this trap from 2014, and there were six mosquitoes for the last week of June in 2014,” Hancock said. “And then I went to the website and found the exact same trap and that trap for the equivalent week of 2023 was 600. We’ve already had a trap up in Greeley. I think it was 3900 mosquitoes.” 

Hancock is an expert on everything involving mosquitos, bedbugs and other blood-sucking insects. Known as the “Mosquito Man” he has made a career of studying and documenting these insects and the climates that sustain them.

Most of his MSU Denver research is conducted at the Mosquito Lab in the Auraria Science Building. He hosts a variety of mosquitos in his lab including the Sabethes cyaneus, a truly mystifying insect that is iridescent in color with two long feather-like paddles that are seemingly suspended in mid-air like an angel’s wings. These mosquitoes are also known to be predatory in their larvae stage—a discovery made by Hancock back in the ‘90s—and can even be prone to eating other smaller larvae.

Chairs and desks are scattered throughout the room for the six to 10 MSU Denver students who work alongside Hancock. The team raises mosquitoes, performs experiments and analyzes the data. Many of Hancock’s lab students also work in mosquito control during the summer collecting traps and logging data.

This year has been the perfect combination of temperature and precipitation to create a sustaining microclimate along the Front Range that is humid yet cool enough for mosquitos to live and reproduce. 

“June of this year was number one in a couple of major metrics in terms of weather, precipitation and temperature,” Hancock said. “We have the highest number of 80-degree or less days and also became number one in precipitation. So it was cool because it keeps a lot of insects alive.”

One thing many people may be wondering after the first reported case of West Nile in Colorado this week is if they have a higher chance of catching West Nile this year. While the answer is probably still yes, it’s a bit more complicated than that.

Not every species of mosquito carries the disease. Historically, Colorado has predominantly hosted the Aedes genus of mosquito which is not a vector of West Nile. The last major outbreak in Colorado was actually in 2003 with a total of 2,948 reported neuroinvasive cases. This was due to an influx of mosquitoes belonging to Culex tarsalis species which is the primary vector for West Nile in the Midwestern and Western United States. It lays its larvae in standing water.

Numbers for reported neuroinvasive cases of West Nile in the last couple of years—omitting 2020 when COVID-19 was rampant and people were more likely to stay inside—have steadily climbed from 96 cases in 2019 to 206 reported in 2022. And while that may seem relatively low, these numbers don’t paint the whole picture. According to Hancock, the majority of cases will go unnoticed unless they produce neuroinvasive diseases like encephalitis or meningitis.  

“Most of the people out there that get West Nile, they don’t even know. So many things make us feel a little crappy,” Hancock said. “I can tell you that Colorado last year with its 206 neuroinvasive cases continues to be high. And this is not a nice rank for us but we’re currently second only to South Dakota.” 

The data that Hancock’s students collect from mosquito traps across the state support this fact and are now showing an overwhelming ratio of Culex mosquitoes in comparison to Aedes. 

“There’s so many Culex right now,” says Hancock. “We don’t see this, this is unprecedented. It’s rare to have Culex be predominant here. We’re breeding a lot of Culex and it’s that rain, it’s just perfect to keep all the water there.” 

Not every Culex mosquito is going to host West Nile. In fact, the vast majority of them don’t. This is because the only way for a mosquito to contract the disease is to get a blood meal from a bird that has West Nile. The disease has quite a long journey to travel before reaching humans. 

“We don’t know how available the virus is going to be from mosquitos. But we do know that there’s more mosquitoes,” Hancock said. “So that alone might mean having more vectors flying around and we already have these [West Nile] positive pools. I bet we’re going to continue to see that number grow.”

According to UC Health, there are many ways to prevent yourself from getting bit by mosquitos, which include getting rid of standing water in yards and avoiding going outside around dusk.

“If you need to be out in dusk, then take precautions, [which] would be light colors, long sleeves, long pants, that’s your best thing. And DEET. That’s all I use if I go for repellent,” Hancock said. 

While intermittently being fed on by blood-sucking insects throughout the day isn’t most people’s definition of a dream job, it is for Hancock and his students. They understand the importance of how these little insects and their behaviors reveal biological information from the world around us, even if it means making a blood sacrifice on the job.

Written by

Logan Kurtz is Bucket List Community Cafe’s engagement manager. He graduated from the University of Colorado Boulder with a bachelor’s degree in journalism and minor in sports media. Growing up on the front range in Arvada, Colorado, Logan spends all the time he can in the wilderness skiing, snowboarding, and mountain biking. You can reach Logan at

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  • I enjoyed reading this biting article. Just last night, while playing with our puppy in the backyard, at least 5 mosquitoes bit me! Thanks for the reminder I need to wear long sleeves and spray myself with mosquito repellent.

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