Casu martzu, sometimes spelled casu marzu, and also called casu modde, casu cundídu and casu fràzigu in Sardinian, is a traditional Sardinian sheep milk cheese that contains live insect larvae (maggots).

The Piophilidae are a family of "true flies", in the order Diptera. The so-called cheese flies are the best-known members, but most species of the Piophilidae are scavengers in animal products, carrion, and fungi. They may accordingly be important in forensic entomology and medical entomology. For a fly maggot, the larvae of many species have an unusually well-developed ability to leap when alarmed or when abandoning their larval food to pupate; they accordingly may be known as cheese skippers or other kinds of skippers according to their food source.