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.
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.
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.”