It can be if you don't have good enough circulation. I made the mistake of covering to much opening on my visions and then had to go back and remove some because there was not enough circulation and I was seeing mold. Not something you want you animals to live in I don't think.
singingtothesnakes
1.1 Normal kids. Well for the most part anyway.
0.1. Worlds coolest Normal Ball Python (Boo)
0.1. Mojave Ball Python (Daisy)
1.0. Pastel Ball Python (Sol)
1.1. Het. for Axanthic Ball Python (Xan and Xab's)
1.1. Garden Phase, Amazon Tree Boa's (Jetta & Izzy)
0.1. Reverse Okeetee Corn Snake (Sarah)
0.0.1. Gopher Snake (Little Bite)
The Ghost did not pan out. shoot!
Hopefully by summer I'll be making payments on a 1.1 lesser
I've always worried about mold too, I've only encountered it when there was a piece of driftwood that was buried under the substrate and started to mold that area, generally I stir the substrate up to check for mold and give it air though, it is a little tough to keep their humidity high enough without covering vents and stuff though, just make sure the air doesn't become stagnant and it should be fine.
I've had BRB's for quite some time now and I never keep the enclosures wet- they're in a 2 x 4 RBI cage with a large water bin - the humidity stays just right!
DON'T over do it with the humidity!
1.1 Brazilian Rainbow Boas
1.0 Anerythrystic Brazilian Rainbow Boa
1.1 Het Albino Red Tail Boas
1.0 Albino motley Red Tail
1.2 Green tree pythons
1.1 Emerald Tree Boas
2.2 Corn snakes
1.3 Honduran Milks (1.1 alb, 0.1 het alb, 0.1 dbl het)
3.4 Ball pythons (Lemon bee, Spider & Pied males. 2 Pastels,poss het pied, girls)