Female mosquitoes bite people in order to get blood so they can reproduce. The female mosquitoes needs the amino acids in blood to make protein for her eggs. Mosquito saliva is injected and the anti-clotting enzyme in it prompts an immune reaction that brings mast cells to the wound. The mast cells release histamine, which causes itching and a red rash. Male mosquitoes do not bite, but spend their time drinking nectar from flowers.
– Provided by The World Almanac 2012