Lord Macdonald's breed. Parasites. Lord Macdonald (son of the Lord of the Isles) once made a raid on the mainland. He and his followers, with other plunder, fell on the clothes of the enemy, and stripping off their own rags, donned the smartest and best they could lay hands on, with the result of being overrun with parasites.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894