What's in mosquito spray? 6 things to know

Pickup trucks spraying fine mist are roaming eastern Fort Collins this week to quash unusually high West Nile virus risk in the city.

Larimer County spent about $10,000 to spray a six-mile area of Fort Collins, from Timberline Road to Interstate 25 between Prospect and Harmony roads, Wednesday and Sunday. The Sunday application will take place between 8:30 p.m. and midnight, the same time frame as the Wednesday application.

The county also sprayed three areas in southeast and north Fort Collins last week. Larimer County now has 10 confirmed cases of West Nile virus for the season, and several more are pending state confirmation, said Katie O’Donnell, Larimer County Health department spokeswoman.

Four cases have been confirmed in Fort Collins, while neighboring Weld County has two confirmed West Nile cases.

1 death reported from West Nile virus in Colorado

Hence all the spraying. For those curious about the mosquito-killing spray used in Northern Colorado, here's a look at six things to know:

1. The spray’s active ingredient is permethrin.

You probably know it as the active ingredient in some over-the-counter flea and tick treatments for dogs. If you’ve ever had lice or scabies, permethrin was probably the active ingredient in any topical treatments you used. Colorado Mosquito Control, which handles spraying for counties and municipalities, sprays the product in an ultra-fine mist with particles about one-fifth the width of a human hair, said Broox Boze, manager of the North Front Range office.

The spray should float in the air for about an hour, killing mosquitoes that come into contact with it. Workers apply the mist at night when mosquitoes are active and pollinating insects are not. Spraying an area greatly reduces the chance of contracting West Nile Virus there for about three weeks, O'Donnell said.

Colorado Mosquito Control lists four permethrin-based sprays in an online explanation of the pesticide products it uses.

2. Permethrin spray is an effective slayer of adult mosquitoes, but not much else.

The spray, when applied properly, usually kills 75 percent to 80 percent of mosquitoes it comes into contact with, but the particles are too fine to kill larger insects like bees or butterflies, Boze said. The spray could kill insects the same size or smaller than mosquitoes, like gnats or small flies. Less than 10 percent of the spray ends up touching the ground, and the product isn’t known to have any residual effects on wildlife or plant life.

3. But maybe stay inside anyway?

Properly-applied spray isn’t known to harm birds or mammals, but Boze still advised keeping your windows closed if you’re in the spray area. If you’re thinking about a late-night stroll but you hear a truck passing your house, wait a few minutes for the mist to dissipate so you’re not walking through the spray.

4. The spray smells a little bit like oranges, apparently.

Our photographer said the spray smells “like chemicals,” but Boze begged to differ.

“People expect it to smell like DEET or something, but it actually smells like fruit,” she said.

5. Colorado Mosquito Control has been working in Fort Collins since May.

Spraying adult mosquito-control products is a rare move that Colorado Mosquito Control only takes when risk of West Nile infection is high. It spends a lot more time using backpacks to spray larvicide near bodies of water to kill as many mosquitoes as possible before they start flying.

6. Larimer County wants to give residents more notice about spraying.

The Larimer County Health Department already notifies people about spraying through press releases, opt-in notifications and the media, but spokeswoman Katie O’Donnell said she gets a lot of requests for signs or flyers in the spray area. That can be difficult because there are only a few days between the decision to spray and the actual spraying, but O’Donnell said she’s trying to find a solution to the time crunch.

FORT COLLINS: First West Nile Virus case confirmed in Fort Collins