Female mosquitoes bite humans to acquire the nutrients in our blood. These nutrients are used to develop mosquito eggs. After a female mosquito bites, she is able to breed and lay eggs.
We call it “biting”, but actually, the female mosquito is piercing your skin like a needle with her proboscis. One tube of the proboscis injects saliva that contains a mix of chemicals to numb pain, thin your blood, and prevent it from clotting. The other proboscis tube sucks up the blood.