The bloodworm is an imitation of the larval stage of the Chironomid midge or buzzer. Bloodworm spend the majority of their time living in a silty tube. When disturbed they move their bodies from side to side.
Best fished either on a floating line and long leader or sinking/intermediate line near the bottom, using a slow figure of eight retrieve.
This is one of the best bloodworm patterns you will find.
This fly is great in red or claret but try other colour combinations including olive, white, pink and yellow, the fish tend to switch off red bloodworms at times and need something else to entice them.