Gnat problem...

Pass week or so I've been having a gnat problem with my reptiles, eventually they went away and I havnt seen nearly as much in their tanks.

Now I have a problem with them in my Sri Lankan tarantula tank. I can see quite a few of them in there, I guess they're getting in through the air vent on the side, it's a Jammie enclosure.

What are some remedies I could do to get rid of them? Maybe something that's common around a house?