It’s the end of mosquito season. What did our experts find in the field this year?

More rain than usual meant more mosquito varieties

We had an above average amount of rain this summer. In early summer, we were seeing a great variety of mosquito species, with multiple species found in a single sample site. This is an unusual finding! We found 11 total species, including:

• 3 species in Aedes genus. Aedes mosquitoes often bite humans but are less likely to spread illnesses in Dane County.
• 5 species in the Culex genus. Certain Culex species can spread West Nile Virus.
• 3 species in other genera, including Anopheles (which carry malaria, but not in Wisconsin!) and Culiseta (an unusual find for our technicians!).

We treated 36 sites for having the potential to spread West Nile Virus

When we find sites that have a lot of larvae with the potential to carry West Nile Virus, we treat the site to prevent the larvae from hatching. The treatment is specifically targeted to only affect mosquito larvae and breaks down quickly in the environment. We treated some sites multiple times if we found repeat larvae.

Mosquitoes are still out, and adult ticks are on the rise, too

Last month, we reported our first human case of West Nile Virus in Dane County

 for the 2024 season. Wisconsin has had over 20 cases total this year, including 3 deaths. Historically in the state, we have seen cases of West Nile in October and even later in the fall. Mosquitoes will most likely remain active until we see steady temperatures below 50°F or a hard frost, which is where temperatures are below 28°F for at least four consecutive hours.

Ticks primarily spread disease during two of their life stages: nymph and adult. In Wisconsin, the nymphs tend to peak around the beginning of summer. Adult tick populations usually come in two waves, peaking once in the spring and once in the fall. In general, if it’s above 40°F, you can expect ticks to be active.

The deer tick (or black-legged tick) is responsible for most illnesses spread by ticks in Wisconsin. Cooler temperatures (around 50°F) are their ideal weather; however, they can be active anytime it is above freezing outside and there’s no snow on the ground.

Take action to prevent bites

If you have outdoor autumn adventures planned, be sure to wear protective clothing:

• Long sleeves
• Pants
• Tall socks
• Light colors (these can make it easier to spot ticks on your clothes)

Use insect repellent while outside, too. Find which repellent is right for you from the Environmental Protection Agency. It’s important to use an effective repellent that has been shown to repel insects.

The Wisconsin Department of Health Services recommends repellent with one of the following:

• 20–30% DEET
• 10–20% picaridin
• 10–20% IR3535
• 30–40% oil of lemon eucalyptus

Get rid of tall grass, brush, and leaf litter from your yard. Make sure there’s no standing water out in the yard either. Don’t forget about your pets! Check animals for ticks after spending time outside. Talk to your veterinarian about tick and heartworm preventatives for your pets. Did you know heartworm is caused by mosquito bites?

You can still pick up one of our tick kits while supplies last! Learn more about illnesses caused by tick and mosquito bites from the Wisconsin Department of Health Services.