Myiasis is a condition in which fly maggots feed off, and develop in, the tissues of living organisms. True myiasis results from files deliberately laying eggs in or on the tissues. There are two forms of myiasis: obligate, in which it is necessary for the maggots to feed on living tissues, and facultative, where files opportunistically take advantage of wounds or degenerative necrotic conditions as a site in which to incubate their larvae. In general obligate myiasis of humans is tropical in origin, whereas facultative myiasis can occur anywhere in the world.