Why Are There So Few Mosquitos In Seattle?

Jun 17, 2014

KUOW listener Nancy Beaudet had a question: Why are there so few mosquitos in Seattle?

As part of our Local Wonder series, we sent our environmental reporter, Ashley Ahearn, onto the muddy trails of the Washington Park Arboretum to find out why skeeters don’t plague Seattle summers.

Ahearn teamed up with experienced mosquito hunter Sharon Collman, an entomologist at Washington State University.

Environmental reporter Ashley Ahearn and a mosquito friend.
Environmental reporter Ashley Ahearn and a mosquito friend.
Credit Courtesy Sharon Collman

Collman, 71, wore bumble bee socks for the excursion.

“You asked why we don’t have mosquitos in Seattle,” Collman said as she headed for the shallow banks of Lake Washington. “The answer is we do. Most places, and anybody who has a home near water will know that. What we don’t have are the kinds that, when you walk in here, there will be 30 on your leg taking a drink at the same time.”

The short answer is temperature. In hot weather, it can take a mosquito egg four to five days to mature to adulthood. In cool weather, it takes two to three weeks.

In Seattle, we don’t have the high temperatures to quickly pump out those generations, Collman said.

Stagnant water – the swampier and steamier the better – also helps mosquitos thrive. In Seattle, waters moves through locks and canals, not soggy wetlands.

We’ve paved most of those.

“You get out into the rural areas where you have more lowlands and ups and downs and swampy areas with little puddles that haven’t dried out yet,” Collman said. “You’re going to have a lot more mosquitos in those kinds of settings.”

Mosquitos need quiet air. They can live among the bushes, but the larvae prefer still water.

“That’s where mosquitoes live,” Collman said. “They like the dark, and they like it humid and they like nice still waters. So those waters right there aren’t going to get a lot of flow traffic.”

Mosquito larvae are called wigglers because of the way they squirm around in the water. When they get bigger and become pupae they’re called tumblers because they look like they’re somersaulting in the water.

Female mosquito, before and after dinner. There are fewer mosquitos in cooler climates, because it takes the eggs longer to mature to adulthood.
Female mosquito, before and after dinner. There are fewer mosquitos in cooler climates, because it takes the eggs longer to mature to adulthood.
Credit Courtesy Sharon Collman

Those are scientific words, by the way. “Yeah, we scientists talk in big words like tumblers and wigglers,” Collman said.

There are roughly 50 types of mosquitos in Washington state. Some are strictly alpine, others feed on reptiles and amphibians only, and some on just birds. Not all are capable of transmitting viruses.

Mosquitos home in on body heat, lured in by carbon dioxide. That’s what distinguishes people from a hot rock. (One study indicates they also prefer people who have just been drinking beer. Make of that what you will.)

As Ahearn and Collman continued their walk, looking for mosquitos, Ahearn asked, “Should we just stand here and breathe a lot?”

“Yes,” Collman said. “Huff and puff.”

And then, success: The sound of a mosquito.

“Eeeeeeeeee.”

The mosquito was unsuccessfully trying to pierce Collman’s jeans.

“Oh, see she’s having trouble getting through the jeans, which is fine with me,” Collman said.

That’s right: The blood-suckers are female. They need the protein from animal blood to build up their egg supply. The males don’t have eggs to mature, so they consume the nectar from flowers.

This mosquito was making that annoying, high pitched sound not to warn Ahearn and Collman, but to attract a mate. Because she wasn't just looking for dinner. She was looking for a date.

Did You Know?

* Only female mosquitos draw blood

* Mosquitos buzz to attract mates

* Mosquitos fly between 1 and 1.2 miles per hour

* Flight range varies; some have traveled up to 30 miles

* In one study, mosquitos were more attracted to the scents of men who had consumed beer than to those who had had water.

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