Mosquitoes don’t suck blood to feed. They suck blood to breed.
Breed, they have – and migrated, too – said Seth Foster, Animas Mosquito Control District manager.
“I always find that insulting when I get bit by a mosquito and I don’t get her and she flies away, because I know that she’s going to make eggs out of my blood,” Foster said.
Keeping the mosquito population of La Plata County in check this year has proved challenging thanks to the migration of mosquitoes of the culex and aedes genuses from mountain elevations up to at least 13,000 feet due to this summer’s shortage of moisture.
So less water means more mosquitoes? That may sound counter-intuitive, Foster said, but it isn’t.
“If you think about it, the mosquitoes just need some damp soil to lay their eggs, and if they don’t have anywhere to lay their eggs, they’re going to go flying,” he said.
Mosquito species that inhabit the San Juan National Forest can fly 20 to 25 miles from where they hatched in search of fertile grounds to lay eggs and produce the next generation of bloodsuckers. They can tolerate wind, survive freezing temperatures and become active as early as February.
“They’re just built different than a lot of the mosquitoes that are down here in the valley or through town,” Foster said. “They’re the ones that ruin your hiking trip pretty quickly if you go off into the trees or go fishing.”
During dry seasons, the mosquitoes – desperate for a place to nest – panic and migrate, he said. Their eggs, embedded in the soil, can incubate for several years before hatching when moisture conditions are right.
Mosquitoes are versatile, resilient insects that out-compete all of their natural predators. If there are 1,000 frogs in a slough, there are 20,000 mosquitoes, Foster said.
The Animas Mosquito Control District must be just as flexible to keep the mosquito population manageable.
The district has acquired a field drone, upgraded its disease testing capabilities and six months ago moved into a new facility, making for quality-of-life improvements for the district staff – about 10 people this year – and the people it serves.
Its service area ranges from Baker’s Bridge north of Durango, Twin Buttes to Durango’s west, Edgemont on Florida Road (County Road 240), Farmington Hill and the Animas City Air Park on La Posta Road (County Road 213) to the south.
Advancing field work
Animas Mosquito Control District has had a busy, challenging season thanks to the migration of mosquitoes from the mountains to La Plata County in search of moist soil to lay their eggs.
The district, however, has made several upgrades to ensure it is prepared in its latest round of an ever-changing fight against one of the world’s most prolific and pestiferous bugs.
A drone has helped the district minimize its impact on natural habitats and properties, said Seth Foster, the district’s manager.
Where crews once had to take amphibious vehicles or trek on foot through soggy fields to spread BTI granules, which creates a film across the water’s surface and consequently suffocates mosquito larvae, they now have the option of flying a drone across the landscape.
“That’s really, really helped us keep the numbers down and protect the public,” Foster said.
Foster said the district has also moved into a new facility at 6525 East Animas Road (County Road 250), adjacent to its old building, to keep up with growth and development in Durango and the county. The move has been a quality-of-life upgrade.
When the mosquito district operations first started in 1961, it operated out of a small trailer on 32nd Street. A gravel pit owner gifted the land for its previous facility in 1988 and the facility was built for $20,000. But there was no insulation or upstairs.
“Hopelessly inadequate, even for the time,” Foster said.
Multiple changes were made over the years to make the space work, but there was never room for equipment. He said people stood “elbow-to-elbow” and ground squirrels often made their way inside and chewed at wires.
Foster said the district is able to store everything under one roof at the new facility. It includes a board room that doubles as staff quarters and houses a lab for testing.
It monitors close to 3,000 storm drains within its jurisdiction, in addition to fields, ditches, wildland space and residences – anywhere standing water could collect and foster the growth of mosquitoes.
Foster said storm drains are sanctuaries for larvae. Natural predators such as dragonfly larvae don’t typically appear there, nor do tadpoles, fish or other creatures that might snack on young mosquitoes.
The district’s top priority is preventing the spread of dangerous and deadly diseases such as West Nile virus and St. Louis encephalitis, which are spread by the culex genus of mosquito. The district’s response time has drastically improved thanks to new genetic testing equipment.
The La Plata County Health Department received its first report of West Nile virus of 2025 in July.
Health Director Theresa Anselmo said last month the patient recovered at home.
Foster said people with strong immune systems typically don’t experience symptoms after contracting West Nile virus. But people with weakened immune systems such as the elderly are at higher risk of severe symptoms and even death.
Earlier this year, Animas Mosquito Control District detected St. Louis encephalitis – which can cause fever, headache, nausea, vomiting and tiredness, in addition to inflammation of the brain for which it is named – near Animas Surgical Hospital on Rivergate Lane along Colorado Highway 3.
Unbeknownst to the people coming and going from the hospital – some of whom have weakened immune systems – a mosquito hotbed laid nearby where specimens turned up positive for St. Louis encephalitis.
The mosquito district found West Nile virus in specimens north of Durango adjacent to a walking trail near a ranch in the Hermosa area.
The mosquito control district quickly neutralized both areas upon detection of the diseases.
Foster said newly acquired technology has reduced the time it takes to identify a mosquito-spread disease from two weeks to two hours.
The gear is called a “polymerase chain reaction” system, or PCR for short, and it essentially “replicates DNA or RNA to detect very small levels of virus,” he said.
Fact and fiction
Animas Mosquito Control District manager Seth Foster said people have the misconception that mosquito control has resulted in fewer bats in La Plata County.
That’s not the case, he said.
He said bats will eat mosquitoes, but the small and agile insects amount to a small portion of a bat’s diet and are hard to catch. The flying mammals prefer fatter, slower prey such as moths.
The limiting of lights during nighttime has also reduced bat encounters – they are attracted to light because insects gravitate toward them and bats are able to easily feed.
“We welcome all the bats that we can get,” Foster said.
People also have the misconception that the mosquito control district is killing off pollinating insects when it deploys mosquito fog, he said.
“We’re doing everything that we can to protect bees. Our products aren’t killing bees in the water, and then when we do have to do a nighttime fog run, we’re making sure not to do properties that have a beehive,” he said.
He said mosquito fogging occurs at nighttime when bees and other insects such as dragonflies are dormant. By dawn, the residual mosquito fog is minuscule and has deteriorated and isn’t a danger to bees.
“It’s all about timing to kill the mosquitoes and keep everything else,” he said.
Many COVID-19 tests were performed around the country using the same technology.
Results are run multiple times, Foster said, but generally, the PCR system provides results much sooner than sending tests to a faraway lab for confirmation – which also occurs for confirmation.
Foster said the mosquito district has run about 25 tests this year, each on a mosquito from the culex genus, the vector of West Nile virus and St. Louis encephalitis.
In the past, it took the mosquito control district two weeks to confirm West Nile virus in mosquitoes at locations such as the La Plata County Fairgrounds, adjacent to the Animas River Trail frequented by people of all ages.
He said he is working with the health department to communicate when disease-positive mosquito hotbeds are discovered, which could help with early diagnoses of patients with relevant symptoms.
“I love mosquitoes and I hate what they inadvertently do,” he said.
He said mosquitoes don’t realize when they are infected with a virus – they just want blood for its protein to lay their eggs and go on their way.
Female mosquitoes specifically require protein from blood to produce their eggs – males do not seek out blood at all and are strictly pollinators.
Females typically bite humans near the end of their active season in September, Foster said.
The mosquito district goes door-to-door all season educating residents about mosquito prevention. It boils down to removing standing water. Next week, the district will begin withdrawing traps and preparing for trail maintenance.
Mosquito mitigation simply requires shaking tarps after rains, emptying tires and anything else that collects water. Fish in a pond goes a long way. Foster said people who collect rain water should cover their barrels with fine mesh to keep mosquitoes out.
“We get some rain and then that’s where you get the container breeders that are just kind of sneaky, and people aren’t even aware of them because they don’t swarm you in your backyard,” he said. “You might get a bite here and there, think nothing of it, but all it takes is one bite.”
cburney@durangoherald.com
