Blood worm or bloodworm is an ambiguous term and can refer to:
- The larvae of a non-biting midge (Family Chironomidae) containing hemoglobin
- The polychaete Glycera, often used for fishing bait
- Species of the Polychaeta subclass Scolecida.
- Lumbriculus variegatus, more commonly called blackworm, but often misnamed by pet stores
- Strongylus vulgaris, a common horse parasite
- Angiostrongylus cantonensis, a parasitic nematode that causes of Angiostrongyliasis and the most common cause of eosinophilic meningitis