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