An Invasive Disease-Carrying Mosquito Has Spread to the Rocky Mountains

This communicative originally appeared connected Inside Climate News and is portion of the Climate Desk collaboration.

It tin transportation life-threatening diseases. It’s hard to find and hard to kill. And it’s obsessed with quality blood.

The Aedes aegypti is simply a taxon of mosquito that radical similar Tim Moore, territory manager of a mosquito power territory connected the Western Slope of Colorado, truly don’t privation to see.

“Boy, they are locked into humans,” Moore said. “That’s their humor meal.”

This mosquito taxon is autochthonal to tropical and subtropical climates, but arsenic clime alteration pushes up temperatures and warps precipitation patterns, the Aedes aegypti—which tin dispersed Zika, dengue, chikungunya and different perchance deadly viruses—is connected the move.

It’s popping up each implicit the Mountain West, wherever conditions person historically been acold excessively harsh for it to survive. In the past decade, towns successful New Mexico and Utah person begun catching Aedes aegypti successful their traps twelvemonth aft year, and conscionable this summer, 1 was recovered for the archetypal clip successful Idaho.

Now, an aged residential vicinity successful Grand Junction, Colorado, has emerged arsenic 1 of the latest frontiers for this troublesome mosquito.

The city, with a colonisation of astir 70,000, is the largest successful Colorado westbound of the Continental Divide. In 2019, the section mosquito power territory spotted 1 wayward Aedes aegypti successful a trap. It was odd, but the mosquitoes had already been recovered successful Moab, Utah, astir 100 miles to the southwest. Moore, the territory manager, figured they’d caught a hitchhiker and that the harsh Colorado clime would rapidly destruct the species.

“I concluded it was a one-off, and we don’t person to interest excessively overmuch astir this,” Moore said.

But then, a fewer years later, it happened again. They recovered 2 much of the invasive mosquito taxon successful traps successful 2023.

“Coincidence is not a connection you usage overmuch successful science,” said Hannah Livesay, biologist astatine the Grand River Mosquito Control District, which is based successful Grand Junction.

The squad bought antithetic traps and adjusted their techniques to hunt for the mosquito. Scientific lit and mosquito researchers told them the effort was bound to beryllium pointless. It was improbable the mosquito would marque it done the winter.

Then, the results started coming in. In 2024, the archetypal twelvemonth of the Aedes aegypti surveillance program, the territory caught 796 adults and recovered 446 eggs.

These mosquitoes weren’t conscionable surviving successful Colorado—they were thriving.

Dengue Virus Driven by Mosquitoes’ Expansion

Mosquitoes are often called the astir unsafe taxon connected the satellite for their quality to dispersed life-threatening diseases to humans. Of those, malaria, carried by pistillate Anopheles mosquitoes, has agelong been 1 of the astir devastating.

However, arsenic clime alteration allows the Aedes aegypti to determination northward, past astatine higher elevations and enactment progressive for longer into the fall, dengue microorganism is accelerated emerging arsenic 1 of the astir unsafe of the world’s diseases transmitted by mosquitoes and ticks, researchers say.

Between 2000 and 2024, dengue cases reported to the World Health Organization accrued much than twentyfold, arsenic clime change, urbanization and planetary question and commercialized pushed the mosquito vector for the illness into caller areas. Climate alteration has besides lengthened the play during which the insect tin breed and thrive successful areas wherever it’s endemic. About fractional the world’s colonisation is present astatine hazard of dengue, according to the WHO, and betwixt 100 and 400 cardinal infections hap each year.

The microorganism is often mild oregon asymptomatic, but for immoderate people, it tin go severe, truthful achy that it’s nicknamed “break-bone fever.” It tin adjacent beryllium deadly. More than 2,500 dengue-related deaths person been reported globally successful 2025, with outbreaks successful Brazil, India, Australia and different countries. In the US, dengue is astir communal successful Florida, wherever the Aedes aegypti mosquito has thrived for centuries successful the subtropical and tropical climates.

In Colorado, authorities aesculapian entomologist Chris Roundy said that portion the mosquito is successful Grand Junction, the state’s nationalist wellness officials are not excessively disquieted astir illness spread—yet.

“The beingness of those mosquitoes does not mean that dengue is going to beryllium there,” Roundy said.

For the mosquitoes to dispersed disease, they request to provender connected a quality who is already sick: Someone who traveled to Florida, contracted dengue and past returned to Grand Junction portion they’re inactive infected, for example.

In different words, the chances of an outbreak of dengue oregon different of the diseases the Aedes aegypti carries successful occidental Colorado stay beauteous slim. Still, helium said, “we are keeping a precise adjacent oculus connected [the mosquitoes] to spot if they grow their country successful Grand Junction, oregon if we commencement seeing them successful different counties.”

The Hunt for Aedes

On a lukewarm and sunny October greeting successful Grand Junction, David Garrett, squad pb for the Grand River Mosquito Control District’s Aedes aegypti program, parked his achromatic motortruck connected what the squad calls their “epicenter street” successful the aged residential vicinity of Orchard Mesa, wherever the Aedes aegypti recovered a foothold successful Colorado.

It was postulation day.

Across the remainder of Colorado, mosquito power operations aimed astatine preventing the dispersed of West Nile microorganism are winding down. Populations of the autochthonal Culex tarsalis mosquitoes, the superior vector for the virus, were declining rapidly successful the autumn chill.

But successful Grand Junction, Garrett is inactive successful the tract looking for the invasive mosquito taxon that seems to get progressive successful the fall.

The traps request to beryllium adjacent to humans—the nutrient source—and an inviting spot for the mosquitoes to laic eggs. Unlike the mosquitoes that are autochthonal to the Western Slope, which breed successful lasting h2o similar ditches and ponds, the Aedes aegypti mosquito prefers to breed successful containers similar potted works saucers, watering cans, and decorative gait fixtures. The traps for them look similar unassuming achromatic integrative buckets with an oddly shaped funnel attached to their tops. The territory has snuck them into corners of beforehand yards, betwixt bushes and on fences passim the neighborhood.

Garrett plucks retired the sticky papers that person been wrong the traps for the erstwhile week, replaces them with cleanable sticky papers and adds a spot of caller water. He’ll instrumentality the samples backmost to the laboratory to number however galore Aedes aegypti they snagged.

But earlier doing that, helium paused to peel 1 of the sticky papers isolated and counted 4 invasive mosquitoes stuck to it. Their pitchy achromatic bodies with reflective achromatic markings are casual to differentiate from the dusty brownish of the autochthonal godforsaken mosquitoes.

As of mid-October, the territory had caught 526 big Aedes aegypti mosquitoes successful 2025, each successful the Orchard Mesa area.

The mosquitoes don’t laic each their eggs successful 1 basket. They skip from instrumentality to container, laying a fewer eggs successful each. “You don’t find 1 and find them all,” said Livesay, the district’s biologist. “So, it’s truly hard to way them down.”

Back successful the car, power territory unit coiled done the neighborhood. From the rider seat, Livesay pointed with a frustrated suspiration astatine an aged tyre lying successful a yard. “Tires are 1 of the astir communal places you find them,” she said.

The species’ penchant for backyards and gardens makes it incredibly hard to control, Livesay said. The territory had to get support from dozens of homeowners successful the Orchard Mesa country to acceptable up and support traps connected backstage property, and lone a fistful of homeowners person allowed them to spray insecticides successful their yards.

Public consciousness of the mosquito’s presence, and the imaginable wellness hazard it could pose, has been gradual; the territory has passed retired fliers and chatted with residents, but the run doesn’t look to person rather taken root. On the time the squad checked its traps, respective residents said that they weren’t alert that an invasive mosquito was contiguous successful their neighborhood.

The caller taxon is besides costly to control: It has outgo the territory astir $15,000 this twelvemonth successful caller traps, further unit who indispensable enactment aboriginal into the play and antithetic insecticides aft learning that the mosquitoes had a absorption to the 1 they usage for the autochthonal mosquitoes—permethrin.

Given however costly it is to power them, further enlargement of their scope connected the Western Slope is Moore’s biggest concern. Right now, the Aedes aegypti occupies astir 100 acres of the Orchard Mesa neighborhood. He doesn’t privation it to summation immoderate much ground.

“If we can’t get escaped of them, oregon astatine slightest confine them,” Moore says, “that’s a immense crippled changer for us.”

“We Need a Cold Winter”

While it’s virtually intolerable to cognize however the mosquitoes got into Colorado, experts said, the pathway could’ve been arsenic benign arsenic a Grand Junction nonmigratory bringing location a potted works from retired of state.

Robert Hancock, a mosquito researcher and biology prof astatine Metropolitan State University of Denver, said that, since the mosquito follows humans and is easy transported by the containers it breeds in, he’s not amazed erstwhile it pops up successful Colorado and different precocious and acold locations. What does astonishment him is erstwhile the mosquito tin past winters successful those areas.

Hancock noted it’s precocious been recovered to endure the winters successful Utah, California, and Oregon—and present successful Colorado.

“That’s the scary part, due to the fact that it made it to the adjacent summertime successful Grand Junction,” Hancock said, speaking successful his Denver laboratory portion feeding his ain colony of Aedes aegypti, reared for research. (He allows the mosquitoes, which are wholly escaped of disease, to provender connected his ain arm.)

As the clime warms, Hancock said, “Aedes aegypti is performing astatine an extraordinarily precocious level.”

More than fractional of pathogenic diseases tin beryllium aggravated by clime change, a 2022 nonfiction successful the diary Nature Climate Change found.

Livesay, the biologist, suspects the newcomer mosquitoes are wiggling their mode into basements and greenhouses to upwind the Colorado winter, which doesn’t person arsenic galore freezing nights arsenic it utilized to.

Grand Junction had lone 17 days of below-freezing temperatures successful 2024, the fewest connected record, according to information from the National Oceanic and Atmospheric Administration. Typically, the country gets much than 2 months’ worthy of freezing weather. Winters determination have, connected average, warmed 2.2 degrees Fahrenheit since 1970.

“We request a acold wintertime for the mosquitoes to not marque it through,” Livesay said. “Things are hovering conscionable supra freezing, and they’re capable to last.”

This communicative was produced with enactment from the Center for Environmental Journalism astatine the University of Colorado Boulder.