Did you know that the housefly always "hums" in the key of F? The four life stages of the housefly are - egg, larva (maggot), pupa, and winged adult. A housefly goes from egg to adult in 10 days, and a female housefly lays more than 2000 eggs in its lifetime! Houseflies carry more than 100 different types of diseases called "pathogens". Flies feed on decaying matter, by liquifying ingesting solids by regurgitating (vomitting) out its saliva.