Can you describe these creatures any further? The description you gave was rather vague. Are they worm like? Shrimp like? From the description you gave they could be small tubifex worms or daphnia. To get rid of them, whatever they are, as long as they are an invertibrate then a copper based product should work. The copper shouldn't harm the fish in your aquarium, but will harm any other invertibrates in the tank, plants will be fine.

I'be had little worms that take residence on the glass, supposedly from the fishfood. I was assured that they are not only harmless but the fish will pick them off as food.

They may be hydras or planaria worms. These usually show up when you over feed your fish or when ammonia levels rise. The worms are parasitic and can attach themselves to the gills of your fish. If you see them flashing (scratching themselves on ornaments or the gravel) then you may have to treat your water. Look them both up online see if you can match any pics to what you see in the tank. If you use any copper based products, make sure (if you have any) you take your snails out. It will kill them also.