Blood worm or bloodworm is an ambiguous term and can refer to:
Larvae of a non-biting midge (family Chironomidae) containing hemoglobin Glycera (annelid), a polychaete often used for fishing bait Species of the Polychaeta subclass Scolecida Angiostrongylus cantonensis, a parasitic nematode that causes Angiostrongyliasis and the most common cause of eosinophilic meningitis Eisenia fetida, an earthworm adapted to decaying organic material Lumbriculus variegatus, more commonly called blackworm Strongylus vulgaris, a common horse parasite