Worm in sand substrate

[julielynn47]

That's the mystery. I have not added anything new at all except my bristle nose pleco, in over a year. And even then it was new fish, not plants or anything. I don't feed live food either. However they managed to get in there, they are certainly still there. I saw them.... or some of them at any rate. They are an interesting addition for sure

 

[WhistlingBadger]

Those critters might have been hiding out in your substrate for months or years without your knowing they were there. Maybe they came in at the start and are just now big enough to notice. Or maybe some change in conditions sent them to the surface. Substrate is a living thing that changes over time, afterall.