I got a terrarium kit as a work leaving gift 3.5 years ago. There’s a colony of nematodes just chilling in there.

How long would such a colony feasibly be able to survive? Will it have a lasting effect on the plants in the terrarium?

Also could someone please explain what the slime is on the inside of the bottle? Wondering if it was something I did wrong when filling and if it can be avoided were I to make another one in future.