Why do mosquitoes leave welts on the skin when they bite?
When the female mosquito pierces the skin for her “blood meal”, she injects a small amount of saliva into a capillary, the blood vessel closest to the skin. The saliva makes penetration of he proboscis (mouthparts) easier and prevents the blood from clotting. Welts or red bumps that may appear after the bite of the mosquito are actually an allergic reaction to the saliva. Some people are more allergic to mosquito saliva than others and tend to welt up more. Some people may be more allergic to specific species of mosquito than other species. The swelling and itching may last from a few hours to a few days. Occasionally individuals may be highly sensitive to mosquito saliva and swell significantly, even to the point where they need medical attention. In any case, people should avoid scratching these wounds, as bacteria from the fingernails may be introduced into the wound and cause infection.
