All flies are insects of the order Diptera, so they lay eggs from which larvae are born which, after various moults, turn into pupae and then into adults. The most known species of gnats is probably the Drosophila melanogaster (fruit fly). Adults are attracted to rotten fruit, vegetables and all the substances in the process of fermentation. This is where they lay their eggs, so that the hatching larvae can easily find something to eat. They have a life cycle that lasts about two to three weeks and reproduce only once in their life. These gnats are bred in many laboratories that study genetics, because they can be bred hundreds of them together in a small glass tube, feeding them with a fruit purée.