Gave the plants and their pots a thorough inspection, nothing on the leaves, nothing under the leaves, nothing on the stems. I gave the surface soil a good going over as well... nothing.
I raked my arm over every inch of the mylar coated walls of my grow cabinet, fingered every crease and cranny. If he'd crawled under there he won't be crawling anywhere else anytime soon.
I haven't actually noticed any further damage or white spots appearing so he may not've stuck around after his first meal, either that or I unwittingly did him in with a previous watering or soil check.
There aren't any open windows in the room my box is in, and I don't think I've ever seen a bug (outside of the occassional spider) in that part of the house.
Anyway, I'm rambling and it doesn't seem like there's a great deal else I can do other than keeping an eye on things. Thanks for all of the advice.