Mosquitoes bite humans primarily because female mosquitoes require blood to produce eggs. The proteins and nutrients in blood, particularly from mammals like humans, provide essential components for egg development. Only female mosquitoes bite, as males feed exclusively on nectar and plant juices, lacking the mouthparts needed to pierce skin.
When a female mosquito bites, she uses her specialized mouthparts, called a proboscis, to penetrate the skin and locate a blood vessel. She injects saliva containing anticoagulants to keep the blood flowing, which often causes an itchy reaction in humans due to the immune response to these foreign substances. Mosquitoes are attracted to humans by cues like carbon dioxide from breath, body heat, and certain chemicals in sweat, such as lactic acid.
This behavior has evolved as an efficient reproductive strategy, with humans being convenient hosts due to our exposed skin and abundance. Mosquitoes don’t rely solely on humans—they bite other animals too—but our proximity and lack of thick fur make us prime targets. This biting also enables them to transmit diseases like malaria or dengue, though that’s a byproduct, not their intent.