The cheese is steeped in history and has been made by Sardinians for hundreds of years. Sans maggots, it’s similar to pecorino: an Italian cheese made from sheep’s milk. The main difference is that after it’s made, a hole is cut in the top and the cheese is placed outdoors where cheese flies (Piophila casei) can find it and use it as a cheap hotel room for trysts and baby making.
Why would you want flies to lay eggs in your cheese? Well, the eggs hatch to become maggots and these larval flies eat the cheese, leaving behind excretions of pre-digested fats, proteins, and sugars. Basically, the larvae are fermenting the cheese to an extreme degree. While cheeses that are aged in ways we’re more familiar and comfortable with tend to lose moisture while developing flavor, casu marzu becomes very soft as it develops flavor.