A mosquito is a tiny flying insect, about the size of a grain of rice, known for its itchy bites and annoying high-pitched buzz. Female mosquitoes pierce your skin with needle-like mouthparts to drink a small amount of blood, which they need to produce eggs. Male mosquitoes don't bite at all: they drink nectar from flowers instead.

That itchy bump you get after a mosquito bite isn't from the bite itself. When a mosquito drinks your blood, it injects a bit of saliva that stops your blood from clotting. Your body recognizes this saliva as foreign and sends chemicals to fight it, causing the swelling and itching. Scratching makes it worse because it spreads those chemicals around and can even break the skin.

Mosquitoes have existed for over 100 million years and live almost everywhere on Earth except Antarctica. While they're mostly just annoying in places like the United States, mosquitoes are actually one of the world's deadliest animals because they can spread serious diseases like malaria, dengue fever, and yellow fever when they bite. Scientists estimate that mosquito-borne diseases affect hundreds of millions of people each year, which is why researchers work hard to control mosquito populations and develop vaccines and treatments for these diseases.