CHICAGO (CBS) — Mosquitoes seem to be everywhere this year. So far nine counties in Illinois have found some infected with West Nile Virus.

CBS 2’s Susan Carlson explains why mosquitoes seem to bite certain people more often and how a common household item can help keep the pests away.

You probably think all mosquitoes are the same. Guess again.

Jim Louderman, an environmental biologist with the Field Museum of Natural History said, “There are about 25 species in Chicago and maybe as many as 50 in Illinois.”

Some mosquitoes eat in the day, others at night. Some only bite animals, while others, of course, like to dine on us.

But did you know that only the female mosquitoes bite?

“Female mosquitoes bite, because they need the protein from blood in order to develop and fertilize their eggs,” Louderman said.

The amount of blood they suck may shock you. Within 30 seconds, they can fill up with about 5 milligrams of blood. That’s about two times their own weight. It’s the equivalent of a 150 pound man drinking a 300 pound milkshake.

Louderman said there’s a way to tell the difference between a male and female mosquito.

“The male mosquito has real feathery antennae, the female doesn’t.”

Alexandra Westrich with the Chicago Department of Public Health says, “Culex mosquitos are different because they breed in standing water, stagnant water, so any kind of small containers.”

Whether you get bit has a lot to do with your personal chemistry.

Louderman says, “the more carbon dioxide you produce, or the higher your respiration rate, you’re more likely to attract mosquitoes.”

Also, some people emit hormones that mosquitoes are drawn to. The insects are also attracted to uncovered skin and body heat, but you can protect yourself.

In addition to wearing long sleeves and loose, light-colored clothing, you can also ward off mosquitoes with dryer sheets, like Bounce. They don’t like the scent.

Another natural repellant is lemon eucalyptus oil.

Louderman says other natural options include, “things like planting marigolds, basil and some of the other herbs help keep mosquitoes away from the patio.”

Mosquitoes only live 7 to 14 days, but the females spend about four days of their lives searching for blood. Each female mosquito will fertilize between 150 and 300 eggs.

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