I wonder if there is any possibility that the cleaner’s employer is also in some way complicit.
Cleaner: “Ooh, those pot plants are lovely.”
Employer: “Just take one … we kind of own them … because they are on common property …”
I would be sending a letter to the strata committee stating that you have seen an unnamed employee of an unnamed resident stealing a pot plant from common property and that the resident has refused to have the plant returned. Can the committee investigate the potential for installing security cameras to protect other residents from theft.
That should put the caterpillars among the pot plants.