It is a mere flea-bite. A thing of no moment. Thus, a merchant who has suffered loss by speculation or failure might say that the loss is a mere flea-bite to him. A soldier might call a wound a mere flea-bite. A passing inconvenience which annoys but leaves no permanent injury. Mr. Disraeli spoke of the national debt as a mere flea-bite.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894