A maggot is the larvae of a fly.  Anglers use maggots usually provided by commercial suppliers to catch non-predatory fish.

Maggots are the most popular bait for anglers in Europe. Anglers throw handfuls into the "swim" they are targeting, attracting the fish to the area. In North America, maggots have been used primarily as ice fishing bait; recently, however, anglers have started using them year-round.