MINNEAPOLIS (WCCO) — Now that the weather is finally warm enough to head outside without a long-sleeved shirt or pants, the mosquitoes, ticks and black flies have appeared.

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“They always bite my ankles,” said one woman sitting in a Minneapolis park Tuesday afternoon. “They love my ankles.”

That had us wondering: Why do bug bites itch?

According to Jim Stark, the executive director of the Metropolitan Mosquito Control District, we’re allergic to the mosquito saliva.

While male mosquitoes are vegetarians who feed on nectar, female mosquitoes bite humans. They need human blood as nutrients to develop their eggs.

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“When the female mosquito feeds on us, she gives off a little saliva,” Stark said. “That saliva acts as a coagulant to keep the blood flowing readily.”

Once our body recognizes something foreign is present, it releases histamine, which causes our blood vessels to swell, hence the redness and irritation.

“There are proteins in their saliva that are irritants to our skin, and we have a little allergic reaction to that,” Stark said.
Mosquitoes reach the human blood by using their straw-like mouth part to puncture the skin to get to the blood vessels underneath. Ticks stick their mandibles into the skin and black flies slice open the skin.

“The black fly will make a little incision into your skin and then sponge the blood,” Stark said.

Scientists still haven’t figured out why some people are more susceptible to bug bites. They do know mosquitoes are attracted to the carbon dioxide in our breath and the lactic acid in our sweat and skin. They’ve also found a genetic link when it comes to reactions to bug bites, but they don’t know exactly why some people’s body smells are better at masking those attractive compounds to throw off the mosquitoes.

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“If you could develop a repellent that is good at that, you’d be making a lot of money,” Stark said.

Heather Brown