Dear Juan Simon,

The deadliest animal on Earth isn’t a shark or a bear. It’s an insect. Mosquitoes kill way more people than any other animal.

I talked about it with Jeb Owen. He’s an insect scientist at Washington State University.

He told me mosquitoes are dangerous because of the way they sometimes eat.

“Through blood feeding, mosquitoes can transmit pathogens that make people and animals sick,” Owen said.

Mosquitoes don’t eat blood all the time. They usually drink fruit juice or nectar from flowers. That’s all male mosquitoes ever eat.

But female mosquitoes need protein to make the eggs that will become baby mosquitoes. They get it by drinking blood from animals like us.

A female mosquito’s mouth—called a proboscis—has six stylets. You can think of them as needles. Two needles have little teeth. The mosquito uses them to saw into your skin. You probably can’t feel it because the teeth are super tiny and sharp.

Plus, the mosquito uses another needle to drip saliva into the bite. Mosquito spit numbs us and makes our blood flow more easily. The mosquito uses two more needles to hold the bite open. Then, the last needle finds a blood vessel and slurps up the blood like a straw.

This is an Aedes albopictus mosquito. The blue arrow points to her proboscis. Sometimes these mosquitoes pass on a disease called West Nile Virus. Photo: CDC/ James D. Gathany, arrow added by Dr. Universe

That’s gross to think about and leaves you with an itchy bump. But it doesn’t really harm you.

Unless the mosquito spit contains a pathogen—sometimes called a germ. That’s a disease-causing microbe that can hitch a ride with the mosquito. It could be a virus, bacteria, a parasite or even a worm.

People can get sick when a pathogen gets inside a mosquito bite.

That can happen two ways. A pathogen can stick to a mosquito’s proboscis. Then, it can fall into the bite as the mosquito feeds. That’s called mechanical transmission.

The second way is biological transmission. That happens when a mosquito eats blood with a pathogen in it. The pathogen changes and makes copies of itself inside the mosquito’s gut. Then, it travels to the place where the mosquito makes saliva. If the mosquito feeds after that, it spits the pathogen into the bite.

Some mosquitoes that carry disease have adapted to live near humans. Instead of laying eggs in ponds or lakes, they lay eggs in containers. Like flower pots, bird baths or puddles. Or trash that fills up with rain water.

That makes it easy for these mosquitoes to bite people—because they’re basically neighbors. It makes it more likely they’ll pick up and pass on pathogens. That’s why scientists work hard to protect people from disease-carrying mosquitoes.

But most mosquitoes don’t bite people or carry disease. They have important jobs in nature like pollinating flowers and being food for other animals. Baby mosquitoes help keep waterways clean. They gobble up algae and other stuff in the water.

Owen told me that studying mosquitoes helps scientist discover new medicines. Like learning how mosquito saliva numbs us and makes our blood flow easily.

Most of all, mosquitoes are just animals sharing our planet. Having a wide variety of life makes Earth better.

Even if some deadly animals keep us on our mosqui-toes.


Dr. Universe