Soft, shapeless worms from the Regulus system, remembered chiefly because the Klingon Korax compared humans to them, and later kept for medical use by Doctor Phlox.
Regulan bloodworms are invertebrates native to the Regulus system, described as soft and shapeless. They are first mentioned in The Trouble with Tribbles, where the Klingon officer Korax tells Chekov and Scotty that Earthers remind him of Regulan bloodworms, one of a string of insults that ends in a bar brawl on Deep Space Station K-7.
The worms turn out to have a practical side. In Star Trek: Enterprise, Doctor Phlox counts them among the many living creatures he keeps in sickbay for their therapeutic properties, a typically Denobulan approach to medicine that his human shipmates find hard to stomach.
The insult is heard again when the crew of the Defiant travel back to the station in the Deep Space Nine episode Trials and Tribble-ations.