A gnat is sometimes also called a blackfly, even though it can be black or gray. It is a very tiny insect, no bigger than the head of a pin. Gnats are found anyplace in the world where there is a river or stream, because they lay their eggs in watery places. They need the blood of warm-blooded animals to survive. They can bite humans right through their clothes to get blood.
A person who gets bitten by a gnat may not even know it at the time. But soon after, the area around the bite will start to swell up. There may be a little bit of blood coming from the bite. The bite will be very itchy and can be painful.
If you've been bitten by a gnat, wash the bite with soap and water. Because gnats can pick up bacteria from other things they've landed on (like rotten food or dead animals), it's also a good idea to swab the bite with a little antiseptic. Putting an ice pack on the bite can also make it feel less painful.