Casu marzu is a traditional Sardinian sheep milk cheese, notable for containing live insect larvae. It is found almost exclusively in Sardinia, Italy.

Casu marzu is created by leaving whole Pecorino cheeses outside with part of the rind removed to allow the eggs of the cheese fly Piophila casei to be laid in the cheese. A female P. casei can lay more than five hundred eggs at one time. The eggs hatch and the larvae begin to eat through the cheese. The acid from the maggots' digestive system breaks down the cheese's fats, making the texture of the cheese very soft; by the time it is ready for consumption, a typical casu marzu will contain thousands of these maggots.

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