Retracting and sealing self in?

[tweenytwinkies]

Are my snails sick? Also help me identify them. 
First i want to go over the most important thing I need help with, my snails aren’t very active as they used to be and now they have closed themselves in with a white seal. I have a temperature and humidity gauges to keep regulated.. but they seem unhappy now. They eat some of the food I give them but they won’t eat bananas or tomatoes and they left it to rot now gnats are there. Are the gnats bothering them? Am I doing anything wrong? 

Now to help identify my babies, I live in Texas and they are land snails. They are Spherical-ish.
heres a image of them that I’ve posted already. On snail pics
they look similar to milk snails but I want to be 100% sure. 

please help as soon as possible 

[pasi9]

I've not had gnats in my habitat, but I guess it's possible they are bothered by them, if there's a lot. I'd probably try to get rid of them anyway though, if I were you.

If you're not sure what kind of snails they are, is it possible that the temp/humidity is wrong for their species? Has anything changed in the way you keep them?