Answer: Cheese mites! Specifically Acarus siro, the mites used to create the very distinctive crust and taste of this French cheese called Mimolette. Mimolette cheese is colored with annatto to provide its cantaloupe" orange color, while the mites are intentionally introduced to the external surface to provide its gray crust. The mites are thought to add to this cheese's distinctive parmesan-like flavor.
Despite some over-hyped media reports, the Food and Drug Administration has not actually banned the importation of Mimolette cheese into the United States. However, there have been reports of halted shipments at the border due to failure of the cheese to meet regulations due to excess of mites on the cheese. I couldn't find any reference to this on the FDA's web page, but here is a good report from National Public Radio.