A fly is an insect that lays eggs in meat which then turn into maggots and then as an adult fly away to eat and make more. Flys eat almost any food and to do it they vomit over the food item and suck up the remains. Flys have a compact and fairly heavy oval body that is sometimes covered with a coarse fur.
Mosquitos have very thin bodies, longer legs and longer thinner wings. The females have a long proboscis (nose) hose that they insert into skin to suck up blood which is used to nurish their eggs. They lay eggs on top of still water in little bubbles. The eggs hatch and the little mosquitos swim around in the water and the adults take flight to do the cycle all over again.