Sounds like someone planted those. Probably an angry vegan...
No, probably not. Under the meat/seafood/deli display you see are stainless steel lids protecting the refrigeration equipment underneath.
That’s the unseen JUNGLE that only gets looked at once or twice a year for maintenance and cleaning.
A very large grocery chain in Texas last year had a baby crawfish slip thru the cracks and lived a very long time eating food snippets that also fell thru the cracks, was a very large, fine specimen when the tech opened up the case to repair some refrig lines.
Or an employee that's tired of working and wants to go back on unemployment.
I've raised maggots (for aquarium fish food). They are unlikely to crawl up from the floor drain to the meat case. A dead rodent lodged up in the case somewhere is a more likely scenario. Also they should look up. We once had a mouse expire above a ceiling tile, the kind with multiple perforations and the smell was going up and the maggots were dropping down onto my mother's bed.