Imagine a tiny insect that’s not just a nuisance but a potential harbinger of deadly diseases, sneaking into places where it was once unthinkable. That’s the reality we’re facing with the Aedes aegypti mosquito, which has defied expectations and established itself in the Rocky Mountains. But here’s where it gets controversial—could this be just the tip of the iceberg as our planet heats up, forcing us to rethink how we live alongside nature?
Published on November 15, 2025, at 7:00 AM, this piece dives into the alarming expansion of the Aedes aegypti mosquito, a species notorious for transmitting serious illnesses like dengue, yellow fever, and Zika. Experts once believed this mosquito couldn’t survive in the dry, cooler climates of the Mountain West due to its dependence on warm, humid conditions. Yet, against all odds, a thriving population has now taken root in western Colorado.
Take a close look at the photo: Hannah Livesay, a biologist with the Grand River Mosquito Control District, highlights the distinctive white bands on an Aedes aegypti mosquito under the microscope in her Grand Junction, Colorado, lab. This image, captured by Isabella Escobedo, underscores the mosquito’s unique features.
This article was initially featured on Inside Climate News and is part of the Climate Desk collaboration, offering a deeper look into how environmental shifts are reshaping health risks.
What makes the Aedes aegypti so troublesome? For starters, it poses a grave threat by spreading life-threatening viruses. It’s notoriously hard to spot and eradicate, and its relentless focus on human blood makes it a persistent predator. As Tim Moore, district manager of a mosquito control district on Colorado’s Western Slope, puts it, these mosquitoes are fixated on us humans as their primary source of nourishment. ‘They’ve got a lock on people as their meal of choice,’ he explains.
Originally hailing from tropical and subtropical regions, the Aedes aegypti is expanding its territory thanks to climate change, which is elevating temperatures and altering rainfall patterns. This allows the mosquito—capable of carrying Zika, dengue, chikungunya, and other lethal viruses—to venture into new areas. It’s now appearing across the Mountain West, a region traditionally too unforgiving for its survival. Over the past decade, communities in New Mexico and Utah have consistently trapped these mosquitoes, and this summer marked the first detection in Idaho.
Grand Junction, Colorado, a city of roughly 70,000 residents and the state’s biggest west of the Continental Divide, has become the latest battleground. In 2019, the local mosquito control district captured a single Aedes aegypti in a trap. Given that similar finds had occurred in Moab, Utah, about 100 miles southwest, Moore dismissed it as an isolated incident, assuming Colorado’s harsh weather would naturally wipe them out. ‘I figured it was just a fluke, and we didn’t need to stress about it,’ he recalled.
But fast-forward a few years, and in 2023, two more of these invasive mosquitoes turned up in traps. As Hannah Livesay, the district’s biologist, noted, ‘In science, we don’t rely on coincidences.’ To tackle this, the team invested in specialized traps and refined their detection methods, even though experts cautioned that the mosquitoes likely wouldn’t endure the winter.
And this is the part most people miss—their efforts paid off dramatically. In 2024, the first full year of surveillance, they collected 796 adult mosquitoes and 446 eggs. These insects weren’t merely surviving; they were flourishing in Colorado.
The Rise of Dengue, Fueled by Mosquito Migration
Mosquitoes often earn the title of the world’s most perilous creatures because of their role in transmitting deadly diseases. Malaria, spread by female Anopheles mosquitoes, has historically been one of the deadliest. But as climate change enables Aedes aegypti to push northward, endure higher altitudes, and remain active deeper into autumn, dengue is rapidly becoming one of the most formidable mosquito-borne illnesses, alongside those from ticks.
Globally, dengue cases reported to the World Health Organization have surged over twentyfold from 2000 to 2024. Factors like climate shifts, urban growth, international travel, and trade have propelled the mosquito into fresh territories. Warmer conditions have extended the breeding and thriving seasons in endemic zones. The WHO estimates that roughly half of humanity is now vulnerable to dengue, with 100 to 400 million infections annually.
For many, dengue presents as a mild ailment or no symptoms at all, but in severe cases, it causes excruciating pain—earning its nickname ‘break-bone fever’ due to the intense joint and muscle agony. It can prove fatal, with over 2,500 deaths linked to dengue worldwide in 2025, including outbreaks in Brazil, India, Australia, and beyond. In the U.S., dengue is most prevalent in Florida, where Aedes aegypti has thrived for centuries in the warm, humid south.
In Colorado, state medical entomologist Chris Roundy reassures that while the mosquito is present in Grand Junction, public health officials aren’t overly alarmed about immediate disease transmission. ‘Having the mosquitoes around doesn’t automatically mean dengue will follow,’ he says. To spark an outbreak, the insects must bite someone already infected, such as a traveler returning from Florida with the virus.
Thus, the likelihood of dengue or similar diseases erupting in western Colorado seems low for now. Nevertheless, Roundy emphasizes vigilance: ‘We’re watching them closely to see if they spread within Grand Junction or venture into other counties.’
Tracking Down the Aedes Threat
On a balmy October morning in Grand Junction, David Garrett, the team leader for the Grand River Mosquito Control District’s Aedes aegypti initiative, pulled up his white truck on what the crew dubs their ‘epicenter street’ in the Orchard Mesa residential area. This neighborhood has become the mosquito’s foothold in Colorado.
It was time for collection. While mosquito control efforts elsewhere in Colorado are scaling back as West Nile virus season winds down—with native Culex tarsalis populations dwindling in the cooling air—Garrett remains active, hunting for these invasive pests that seem to perk up in fall.
Garrett positions traps near human habitats, where the mosquitoes seek blood meals and egg-laying spots. Unlike local mosquitoes that reproduce in open water sources like ditches or ponds, Aedes aegypti favors enclosed containers such as plant pot trays, watering cans, and garden ornaments. Their traps resemble innocuous black plastic buckets topped with a peculiar funnel. The district has discreetly placed them in yard corners, amid shrubs, and along fences.
Garrett removes the week-old sticky papers from the traps, replaces them, and adds fresh water. He’ll later analyze the samples in the lab to tally the Aedes aegypti captured. On this day, he quickly spots four of them clinging to a paper, their dark bodies with gleaming white patterns standing out from the earthy hues of native desert mosquitoes.
By mid-October, the district had ensnared 526 adult Aedes aegypti in 2025, all confined to Orchard Mesa.
These mosquitoes scatter their eggs across multiple sites, depositing just a handful in each container. ‘You can’t locate one and catch them all,’ Livesay explains. ‘They’re tricky to pin down.’ As they drive through the area, she gestures exasperatedly at an abandoned tire in a yard. ‘Tires are a top spot for them,’ she adds.
Their penchant for backyards and gardens complicates eradication. The district secured permission from numerous Orchard Mesa residents to install and service traps on private land, though only a few agreed to insecticide treatments. Raising public awareness has been gradual; they’ve distributed flyers and engaged with locals, but many residents remain unaware of the invasion.
Controlling this species is also pricey. The district has spent around $15,000 this year on new traps, extra staff working extended hours, and alternative pesticides after discovering resistance to permethrin, the chemical used on native mosquitoes.
For Moore, the district manager, the greatest worry is further range expansion on the Western Slope. Currently limited to about 100 acres in Orchard Mesa, he fears broader spread. ‘If we can’t eliminate or contain them, it changes everything for us.’
The Gunnison River meets the Colorado River just east of the Orchard Mesa neighborhood in Grand Junction, where this invasive mosquito has settled.
The Winter Survival Mystery
It’s unclear how these mosquitoes arrived in Colorado, but experts suggest something as simple as a resident transporting a potted plant from another state. Robert Hancock, a mosquito researcher and biology professor at Metropolitan State University of Denver, notes that since Aedes aegypti travels with humans and breeds in portable containers, its appearance in high, cold spots isn’t shocking. What’s astonishing is their winter survival in places like Utah, California, Oregon, and now Colorado.
‘The real worry is that they persisted through to the next summer in Grand Junction,’ Hancock says from his Denver lab, where he maintains a disease-free colony for study (and lets them feed on his arm). With climate warming, he observes, ‘Aedes aegypti is excelling beyond expectations.’
A 2022 study in Nature Climate Change revealed that over half of human pathogens are worsened by climate change. Livesay, the biologist, theorizes that the mosquitoes are sheltering in basements or greenhouses during Colorado winters, which are milder than before.
Grand Junction recorded only 17 sub-freezing days in 2024, the lowest on record, per National Oceanic and Atmospheric Administration data—far fewer than the usual two months. Winters have warmed by an average of 2.2 degrees Fahrenheit since 1970. ‘We desperately need a harsh winter to stop them,’ Livesay warns. ‘Temperatures are barely dipping below freezing, allowing them to endure.’
This piece was supported by the Center for Environmental Journalism at the University of Colorado Boulder.
What do you think? Is climate change turning the tables on us, making once-rare threats commonplace? Or could human behaviors, like unchecked travel and urban sprawl, be the bigger culprits in spreading these diseases? Share your thoughts in the comments—do you agree that stricter regulations on imports or better community education could curb this, or is this an inevitable outcome we’ll just have to adapt to? And what about the ethical debates around pesticide use—necessary evil or risky overkill? Let’s discuss!