They aren't parasites, probably harmless, and at the worst, a bit annoying. Is this your snake tank with live plants, or one you are setting up for darts? Not that this makes a lot of difference. There are so many little critters that show up in a planted vivarium, one has to learn just to ignore all but those that might be doing some obvious physical damage--like slugs and snails. I even ignore slugs and snails except to pick them off the glass and plants when I see them. The little worms could be about anything from tiny beetle or insect larvae to springtails. Do they flip around at all? Springtails swim around and then leap like bits of popcorn. They aren't really at all worm-like, however. They are not only harmless, but good soil organizers and great dart food. You will get all sorts of "stuff" in a planted vivarium. Nature takes its course, and they are a part of the balance you want to achieve. Soil and water critters will come and go, as do molds and fungi. You don't have to take down your entire tank, sterilize (or sanitize, is a better term,) and start over every time an unknown "worm" crops up, or you would be doing it on a weekly basis. That would totally destroy the concept of a natural tank planted with living plants.
It's impossible to identify every critter we see unless we are entomologists and have the physical faculties to do so. If the animal you have in the tank is initially healthy, it will remain so as long as the conditions of humidity, temperatures, food and vitamins are right for it.
-----
Patty
Pahsimeroi, Idaho
4 D. auratus blue
5 D. galactonotus pumpkin orange splash back
5 D. imitator
6 D. leucomelas
4 D. pumilio Bastimentos
4 D. fantasticus
4 P. terribilis
4 D. reticulatus
4 D. castaneoticus
2 D. azureus
4 P vittatus