Blood worms look less worm-like with a segmented outer shell and have a bright red colour thus their name. They make a tube to live in so as to shield themselves from predators and also for enabling them to hold on to a surface.
Midge fly larvae are most commonly called blood worms. They get their name because they are blood red. The substance that allows them to live under water causes them to be red. Gold fish love blood worms. So if you want to make your gold fish really happy find or buy some blood worms. You can find more information here: http://www.raingarden.us/bloodworms.htm