I've written before about early flea performances but my latest research has been into trying to discover when the first use of the phrase "Flea Circus" was used. My dictionary search had already determined that it was before 1934 when the Hecklers first used the phrase.
Thanks to the Wellcome Library I've managed to remotely access "19th Century British Library Newspapers" and the "17th-18th Century Burney Collection Newspapers".
Not only has that resulted in some definative dates for Boverick, Bertolotto and the Industrious Fleas but it's also turned up an early example of the phrase "Flea Circus".
Back in 1886 the Manchester Times ran a section caled the Childrens Corner, on the 22nd May they published the following:
A Flea Circus composed of about two hundred of the most distinguised and intelligent fleas in the entire family, was exhibited a few years ago. Who first discovered that the flea was susceptible to education and kind treatment is not known; but the fact remains that on their small heads there is a thinking cap capable of accomplishing great results. In the selection of fleas for training, however, the same care must be taken as with human beings, as the greated difference is found in them. Some are exceeding apt scholars, whole others can never learn, and so it is that great numbers of fleas are experimented with before a troupe is accepted. One of the first lessons taught the flea, is to control its jumping powers, for it its great leaps should be taken in the middle of a performance, there would be a sudden ending to the circus.
This in turn references an article in the children's magazine St Nicholas. I've cross referenced this against a contents list for The St. Nicholas Magazine and there on page 533 in volume 13, No 7, May 1886 is "The Smallest Circus in the World" by C. F. Holder, illustrated by J. G. Francis.
The HathiTrust Digital Library has a copy of this edition and tha article is an entertaining read.
So to answer that definative question of "who invented the flea circus", I'd say it was children's magazine writer C.F.Holder in May 1886 as prior to this the performances were described as exhibits or exhibitions. Obviously if someone can find a reference to an earlier use of the phrase "flea circus" then I'd love to hear from you.
Ref: Manchester Times (Manchester, England), Saturday, May 22, 1886; Childrens Corner - Flea Circus
St. Nicholas [v13 # 7, May 1886], page 533