Complex sentence: This acidic environment provides conditions that are ideally suited to bacteria that metabolise cellulose, insects cannot metabolise cellulose so the presence of these bacteria allow cellulose to be metabolised into basic sugars, this provides nutrition to the black fly larva as well as the bacteria.
Split into simpler sentences: This acidic environment provides conditions that are ideally suited to bacteria that metabolise cellulose. This provides nutrition to the black fly larva as well as the bacteria.