Mosquito Abatement (copy)

Vector Biologist Chris Azevedo with Napa County Mosquito Abatement takes a water sample from standing water near Napa Valley Corporate Drive in 2017.  This summer south Napa has been hit hard by salt marsh mosquitoes whose bites are particularly painful.

There’s nothing to like about the salt marsh mosquito.

They have a painful bit that can leave a welt. They like warm weather and daylight hours — exactly the same conditions that attract Napa humans to the out of doors.

This summer is a bad one for salt marsh mosquito bites. So many students in the Napa Valley Unified School District have been bitten since schools reopened two weeks ago that the district had to send out a letter this week explaining to parents what’s going on.

“It’s unusual for a kid to come home with mosquito bites after going to school. That’s made parents think, ‘Humm, what’s happening?’” said Elizabeth Emmett, NVUSD spokesperson.

Wes Maffei, manager of the Napa County Mosquito Abatement District, confirms that this is an exceptionally bad year for this summer biters.

Most years, the district is able to knock down their numbers with a larvicide applied to brackish and salty wetlands where they breed, Maffei said Tuesday.

Salt marsh mosquitoes are most commonly found south of Imola Avenue along the Napa River’s many marshes and wetlands, he said. They proliferate when high tides leave behind breeding pools of water.

“There have been a lot of high tides this year,” Maffei said. Also, because of habitat restoration efforts, there are more wetlands than in decades past.

“All these things add to the mix of what could potentially happen and sometimes does,” Maffei said.

Napa County Mosquito Abatement District has five workers whose full-time jobs are to prevent mosquitoes from breeding, he said. If even a quarter-acre patch in a 100-acre wetland area untreated with larvicide, the numbers of salt marsh mosquitoes can balloon, he said.

“If there were no effort to try and manage this mosquito in the wetlands, there would be clouds of these things,” said Maffei, noting that the journals of the early California pioneers are filled with references to noxious numbers of summer mosquitoes in the Bay Area.

You have free articles remaining.

Become a Member

Fortunately, the salt marsh mosquito does not carry diseases, Maffei said.

In its letter to parents, the NVUSD emphasized that point, noting “this mosquito does NOT carry West Nile virus or any other disease.” But “the bite can be painful and leave a welt.”

The schools most affected by this warm weather, salt-water-loving mosquito are Snow Elementary, Harvest Middle School, River School, Napa Valley Language Academy and “potentially” Shearer School, the district said Tuesday morning.

On Tuesday afternoon, the district added West Park, Northwood and Browns Valley schools to the distribution list.

Maffei said American Canyon has not been hit hard by the salt marsh mosquito, which can travel up to 10 miles, but generally has no reason to do so. North Napa is generally considered beyond this mosquito’s range.

“Neither mowing the grass nor reducing irrigation will reduce the number of mosquitoes, so NVUSD will not take those steps,” the district said. “State law will not allow us to use insecticides on the school campus. So our best option is to wait until the adult mosquito activity is over.”

The district advised that long pants and long sleeves can help protect a child. School officials will monitor conditions on campuses and could decide to keep children off grassy areas or fields, the letter to parents said.

Many people use insect repellents to protect against mosquitoes, but Maffei said he cannot recommend them because of liability issues.

Indeed, Maffei said he’s allergic to repellents, which give him a rash.

He predicted the salt marsh mosquito population will drop soon, particularly with cooler temperatures.

Napa also has year-around mosquitoes that breed in fresh water and do their biting in evenings and at night. Fortunately, none of them bite like the salt marsh mosquito, Maffei said.

Get local news delivered to your inbox!

* I understand and agree that registration on or use of this site constitutes agreement to its user agreement and privacy policy.

City Editor

Kevin has been city editor since September 2010. He joined the Register in 1973 as a reporter. He covered Napa City Hall and assorted other beats over the years. Kevin has been writing his Napa Journal column on Sundays since 1989.