it sounds to me that you just have a couple spiders trying to build webs in the humidity. the webs are getting caught to the side of the terrarium and thats where you get the little white strands.

there is nothing to worry about, they cannot affect your plants in any way.

the only other explanation would be a sort of moss you collected has started growing up the side of the terrarium. i know there are some mosses that do that in fine strings that eventually grow out into more moss.

Sounds like springtails? heres a link, http://www.uky.edu/Ag/Entomology/entfacts/trees/ef420.htm ,they live in the soil and do no harm, theyre cool little critters to have in a terrarium as they do a good job "cleaning house" =) the webing sounds like fungus to me, does it look like something out of a sci fi movie? not quite a spiders web but vainy looking? if so its fungus, wont harm your plants but does sometimes get out of control, get some air circulating in there, maybe run a very small fan, like a computer fan across the top if the terrarium, that should do the trick, make sure you keep an eye on the humidity, dont want to dry out the plants, and if that doesnt work, but it should, and if you dont mind doing it, just take it apart and clean every thing with cool water, then use new sterile potting soil, and redo it =) let us know how it goes =)

I am fairly confident it is webbing- although if i noticed some awesome fungus like that growing i would probably be thrilled! lol.

Aside from looking like any other sort of wiped-up-webbing I've actually spotted a bead-sized little clear spider in there before.

I guess I'm not worried about them hurting the plants, so much as i don't want to end up with a jar full of spiders- or a ROOM full of spiders!

How do i attach a photo to my post so i can show you the little strings that are still on the side of it? Heres a link to the photo at least .

Here is a link that might be useful: PHOTO

Hmm! Interesting update:

Today there is white fluffy stuff on the sides of my terrarium that was facing the window- I took some pictures. Is this really abnormal?

Im worried about what this could be- and would like to wipe it off but if it's just going to come back theres little use.

Here is a link that might be useful: 3 photos of the fluff

Either mold or fungus, try releasing the humidity, do you have a cover on it? if so, take it off and let the humidity escape, it seems that it is to humid and poss why the mold/fungus is growing, along with the good amount of sun its getting from the window, just leave it uncovered till the condensation on the glass is gone, then cover it back up and wait and see if the condensation returns, if it does repeat the process till the condensation doesnt come back, there should then be enough moisture for the plants, but not enough for the moldy gooey messy stuff to return, if it does, you will have to go the first route, letting the air circulate in the jar by letting a small fan blow accross the top of the set up.