The name "blood worm" refers to either the larval form of a mosquito-like insect or the venomous fish bait. The larval blood worm has a cycle of 10 to 12 days before it grows into its adult form. Fanged blood worms do not change form and are similar to leeches.
Both types of blood worms share the same reddish tint. However, the venomous blood worm can grow up to 15 inches long. While these worms are venomous, they are not harmful to humans. Their bite feels like a bee or wasp sting. Blood worms are usually found in damp areas.