Chronon Flea

One of the items on the Dr Smith shelf by 2019 was a report by Giles concerning "the dangers Chronon Fleas presented for archives". When Box attempted to read it, she discovered that it had itself been gnawed at by Chronon Fleas. (PROSE: Out of the Box)

Behind the scenes
Chronon Fleas originate in the Crew of the Copper-Colored Cupids series. There, it was shown that the species' name under the scientific was Siphonaptera Retroannalis. Chronon Fleas were presented as parasites present across the Omniverse, drawn to "dimensionally aberrant locations like temporal vortexes or the Void itself". They had the ability to use any writing concerning such places as a way to return there, destroying the piece of writing in the process.