Mosquitoes bite primarily because female mosquitoes need blood to reproduce. They use the proteins in blood to develop their eggs. Male mosquitoes do not bite; they generally eat flower nectar only. When a female mosquito bites, it uses its mouthparts to pierce the skin, suck blood, and inject saliva. The saliva causes an immune reaction in the bitten person, leading to itching and swelling from the bite.
Several factors attract mosquitoes to humans, including carbon dioxide emitted in breath, body heat, skin odors shaped by bacteria, and even blood type. Mosquitoes use their antennae to detect these cues. For example, they are especially attracted to people with Type O blood and those who emit certain chemicals like lactic acid on their skin. Activities that increase carbon dioxide emission such as exercise or pregnancy can make a person more attractive to mosquitoes. The biological purpose of biting is to obtain blood for egg production, not for feeding on humans generally.
