I find that bloodworms don't seem prolific as mosquito larva,
it can be time consuming removing bloodworms from decayed leaf /plant material one of my water butts containing duckweed had a good number of blood worms, the easiest way to separate worms is to put duckweed into a bucket or container of Freshwater the worms will slowly make the way to the bottom of container I put some duckweed in a small fish tank and left it within 2or3 hours most of worms had gone to the bottom of tank and Bury themselves in mud like caves