It seems the compost I used was more lively than anticipated. There's an earthworm crawling around in there.
It's a decent 12 inch pot, but it's still effectively a limited environment. So I'm not sure if I should leave him in or take him out.
UPDATE: alright. I'll keep him in, cross my fingers, and hope I've pulled in enough of an ecosystem to both sustain him for his expected lifespan, and safely handle the subsequent death and decomposition.
Leave from the pot to earth. They can smell decaying plant matter, and even if it (earthworms are hermaphrodites btw) went over the side, they can easily survive a foot drop. It takes just a minute or two for one to crawl from one side of a sidewalk to another, five or ten minutes to make its way from one side of a patio to another, at a time when most animals that might prey on them (or accidentally step on them) are sleeping. The risk is minimal and no less than any other worm transiting overground to a new site, which is quite common.
It's an indoor plant, so I guess finding it's way out of the apartment would be the challenge.
On a re-read of the post, I don't see it stated either way. While I've definitely made an unwarranted assumption of it being outdoors now you bring it up, I don't think it's definitely indoors either. The textile in the background of the picture is the only real clue I'm seeing, and even that could be the back of some patio furniture. Lighting maybe artificial...
I don't know if earthworms have some reproduction-limiting mechanism for restricted ecosystems. I doubt it, frankly. I don't think there'd be any problems for the plant, but the worms would probably eat themselves to death within a year or so.
It's an indoors office plant. If it ends up leaving the pot, it'll likely end up getting rolled over by some chair wheels.
Given the soil mix I used, it'll likely be very happy for the rest of its life.