These pesky little insects are most unwelcome, especially when you are in the midst of enjoying a delicious meal. These houseflies can be highly detrimental to human health. They feed on foodstuff via the most unhygienic way by salivating on food before ingesting it, thereby leaving bacteria on the remaining food. This can cause the spread of diseases such as cholera, typhoid fever and tuberculosis. The average lifespan of a fly is 1 month, and a female fly can produce more than 500 eggs in 4 days.