Hearing that buzz? It’s the mosquitoes.

Ticks and mosquitoes are out in full-force this summer! We’re concluding our tick and mosquito series with a look at our mosquito monitoring work.

It’s July in Dane County, and you know what that means. Barbeques, beaches, ice cream…. and mosquitoes! It may surprise you to know that not all mosquitoes are the same, and it’s their differences that drive public health interventions.

Not all mosquitoes are created equal.

Did you know there are over 50 species of mosquitoes found in Wisconsin? Many of them do not bite humans; some prefer birds, amphibians, or other species. Culex territans, for example, only feed on frogs, not people. So just seeing mosquitoes doesn’t mean that you’ll get bitten.

Some mosquitoes do not spread disease either. In Public Health, we’re concerned with the mosquitoes that spread disease, like West Nile Virus.

Getting bitten this year? You’re not alone.

Have you ever walked in grass after a big rain and suddenly you’re in a cloud of mosquitoes? That’s a classic move for Aedes vexans, who like to lay eggs in the grass. The eggs hatch when the ground gets wet from a rainstorm. State experts haven’t known Aedes vexans to spread West Nile Virus among humans in Wisconsin, but they do bite, and they are vexing! Our mosquito staff have seen quite a few Aedes vexans this year with all the rain we’ve been getting recently. If you’re getting bitten a lot this year, you can probably blame those pesky flood mosquitoes like Aedes vexans and Aedes trivittatus.

We only kill mosquito larvae that can spread illnesses.

Our mosquito team goes out from Memorial Day to Labor Day to look for mosquitoes at public water sites (such as ponds in parks or city ditches). You can see our findings on our dashboard that’s updated weekly. 

We only sample on public sites in communities that opt into our services through a cost-sharing agreement (municipalities that want to participate in a cost sharing agreement for mosquito surveillance can send us an email to talk).

The mosquitoes we worry about in Dane County are called Culex pipiens and Culex restuans. They’re the species that can spread West Nile Virus in Wisconsin. They like shallow, still, dirty water to lay their eggs, so they’re more common when it’s a drier summer, unlike pest mosquitoes like Aedes vexans.

If we find higher numbers of these larvae species at a site, we will treat the site with a larvicide that specifically targets mosquito larvae. We do not treat sites that have lower numbers of larvae or larvae species that do not spread West Nile Virus.

Why we don’t kill every mosquito

Believe it or not, most species of mosquitoes avoid biting humans! We don’t kill every kind of mosquito larvae because many mosquitoes are important food sources for other animals. Because of their ecological importance, the DNR permits us to only treat species that can transmit diseases to people. Additionally, we can only sample on public sites in communities that opt into our services.

The larvicide we use is bacteria that is very specific to mosquito larvae and can be safely applied to areas used by humans, pets, horses, livestock, birds, or wildlife. But mosquito control efforts haven’t always been so targeted (see image). In the mid-20th century, water sites were often sprayed liberally with pesticides like DDT, which had harmful ripple effects throughout the ecosystem. 

Image credit: National Archive

To protect both people and the environment, our work is only focused on the mosquitoes most likely to make people sick.

You can help us control mosquitoes.

Unfortunately, you probably have a few mosquito breeding sites in your yard, on your porch, or on your balcony. Some mosquitoes only need water the size of a bottle cap to lay eggs in, so even just a little standing water can be a problem. The good news is you can do something about many of them! Once a week, get rid of standing water in:

• Old tires
• Buckets
• Toys
• Leaf litter
• Clogged gutters
• Potted plant trays
• Tarps or covers
• Bird baths
• Anywhere else that collects water

Don’t forget to protect yourself!

As we discussed in our Not Today, Mosquitoes! blog post, the most important thing you can do to protect yourself is use insect repellent. There are many repellent options available. The Wisconsin Department of Health Services recommends using repellents with at least one of the following:

• 20–30% DEET
• 10–20% picaridin
• 10–20% IR3535
• 30–40% oil of lemon eucalyptus (not for children under 3 years old)

Want to read more?

Check out our other blogs with the tick and mosquitoes tags.