There are significant differencies between drain flies and fruit flies. Drain flies are about a 1/6 of an inch in length, their body is completely covered with hairs. They have a pair of antennae that helps them navigate while flying and moving around. You are not really going to see them flying though, as they rather prefer to walk. Fruit flies have either black or red eyes. The rest of their body is pretty much evenly colored except their abdomen, which has dark stripes. While the red-eyed ones are of the same size as drain flies, the black-eyed ones are slightly bigger. Compared to house flies, they are really not as big. They buzz around in the kitchen looking for fermenting leftovers.