Fruit flies and gnats are common pests that can infest homes and cause economic damage to crops. Fruit flies belong to the family Drosophilidae and are characterized by their small size, reddish-brown eyes, and vinegar-like odor. They breed in decaying fruit and can transmit diseases. Gnats, on the other hand, are tiny flies that can vary in appearance depending on species. They often feed on decaying organic matter and can bite humans, transmitting diseases. Fruit flies have been extensively studied as model organisms, leading to advancements in genetics and disease research.