Back before computers, before DVDs, even before television and the movies, when people wanted to kick back and be entertained they went places and saw things. Sometimes they were shows, sometimes clowns, and sometimes they were trained insects.
Flea circuses were small scale shows where actual fleas were fastened to tiny vehicles and forced to race. And other stuff like that. They date back to 1833 and were still operating in places as late as 1970.
If you care to look, check out this website. Or just watch here:
If your hunger for fleas is still running wild, oobject has ten flea circus contraptions for your review.