If you think Moab has been invaded by tourists, just wait until the mosquitoes arrive.
Moab Mosquito Abatement District Manager Libby Nance is predicting a “banner year” for the little biters thanks to heavy snowpack in the Central Rockies that continues to feed the Colorado River with runoff destined to flood the sloughs and other low-lying and heavily vegetated bottomlands representing hundreds of acres along the river and the Scott Matheson Wetlands Preserve.
When the weather warms and the water goes away, leaving a muddy bog, mosquito larvae – eggs that have lain dormant, some for many years – comes to life.
Nance, an aquatic entomologist, said she has to predict how bad mosquitoes might be and that isn’t easy in the face of climate change.
“The one thing we need in this story is to let people know these are not the mosquitoes that cause West Nile virus,” she cautioned. “These are nuisance mosquitoes.” That doesn’t mean they won’t bite – they do, they’re day biters – but they don’t carry disease. The West Nile-carrying mosquitoes will come in later in the summer.” But this species, Aedes vexans, are so-named for their “determined, vexing” behavior.
Still, nobody wants to provide a blood meal to these hunters even if they are only a nuisance.
“Every flood season is different,” said Nance, who was hired to modernize the mosquito district three years ago. “There are so many variables and you only get one chance to get it right.” One predictive clue? The wetter-than-average snowpack. The Central Rocky Mountains were still at 160 percent of normal for snowpack earlier this month.
Nance keeps her focus on the river. “We religiously monitor the Colorado Basin River Forecast Center to predict peak flow,” she said. “Then we have to use our best guess.”
Nance said the closest measuring instruments are upstream near Cisco, where NOAA’s Colorado Basin River Forecast Center is predicting peak flow to be 36,000 cubic feet per second. The river peaked around 22 cfs on May 1, and again just under 20,000 this past Saturday, May 18. Nance expects it to peak again sometime after June 1, expecting it to reach 40,000 cfs. That’s the kind of flow that creates flooding.
The district has four employees, including Nance, and a modest annual operating budget of $40,000 to combat mosquitoes by destroying the larvae before they hatch and head for the city.
It takes cooperation from The Nature Conservancy, which manages the southern half of the preserves, and the Utah Division of Wildlife Resources, which has the northern half. This year, the Department of Energy allowed Nance’s team access to the low-lying river bottom on the UMTRA site.
Modern (Mosquito) Warfare
Larvicide will be applied as workers do “the hottest, sweatiest job you could do.” She said only biological controls would be used with the idea of targeting mosquito populations in the water rather than “on the wing.”
As bottomlands dry out, those that hatch will often migrate up Pack and Mill creeks, looking to hunt and for somewhere to get out of the heat. “They don’t want to be hot, just like us,” she said.
The Matheson Wetlands consume about 1,000 acres. Nance said if most or all of those acres flood, under the perfect storm conditions she believes are likely to develop, Moab could see “astronomical” numbers.
The district in the past has seen larval densities of 3,000 per square foot in Moab at uncontrolled river flood sites. That’s more than 130 million larvae per acre – and 130 billion at the wetlands to use the absolute worst-case scenario.
Nance has acquired motorized backpacks to make her tiny crew – two work the wetlands and the third has the valley – far more efficient. The backpack can spray larvicide in a 70-foot radius, allowing them to cover an acre in about 15 minutes rather than the hours it took in past years when the work was done by hand.
They don hip boots, long-sleeved shirts and long pants. They go through some rough country, said Nance, and perform “hot and hard physical work.”
Not only can they cover more ground much faster than before, new products Nance has purchased are effective up to 30 days rather than 5, giving residual control. She hopes the work will get easier in the future. Nance plans on obtaining a drone that can carry a larvicide payload. Her employees will train on its proper operation.
Nance said there are 18 separate mosquito species in southeastern Utah; one third of them are worth worrying over – three nuisance and three vector species – which are those that carry diseases. The remaining dozen are either rare or are not mammal feeders.
She wants people to be patient with the abatement district and she knows she’s going to get called out to fog, but that likely won’t happen during this nuisance mosquito season that could start and end sometime in June or creep into July before its three-week lifespan comes to a close. For one thing, fogging will do little good in the wetlands. For another, the fog is an indiscriminate killer of insects. Larvicide kills only mosquito larvae.
“We have a mission to protect public health,” she said. “And that’s what we’re doing.” She’s called local outlets that sell mosquito repellant products and advised them to stock up. She said people can spray their shrubbery for mosquitoes, “just make sure you purchase a product labeled for mosquitoes,” she said.
Nance expects the proactive effort she and her staff have put forth to pay dividends, but she’s understandably nervous about the unknown, saying with arms spread wide, “I’m as prepared as I can be.”