I was under the impression that flea circuses were pure illusion—there were erratic, untrained fleas, or no fleas at all—and the entertainment was provided solely in the mind of the audience. The article seems to suggest otherwise. If it had been published a day later I'd swear it was a joke.

The author says that the real attraction of flea circuses included "seeing insects in costumes, pulling carriages, or racing each other." Is he seriously suggesting that fleas were somehow wrangled into miniature suits?

The article concludes with the head-patting remark that the Victorian credulity about flea circuses is "humorous, but not surprising." It's not clear to me that the joke isn't on moderns who believe in that type or degree of credulity from our comparatively recent ancestors.