Maggots in your skin?
The botfly is a large fly - like a twice-sized housefly. The larvae - maggots - of this fly grow inside the skin of animals such as livestock - and humans!
These maggots will move in the skin as they grow, and will cause significant pain before they climb out of the skin as large maggots.
The life cycle of the botfly is clearly told in a video by Animal Planet.