I bought some guinea pig food from Wal-mart. A few days later, I noticed a few moths in my room.
This problem escalated to the point where i would vacuum up 10 moths, and an hour later, there would be 10 or so more moths. I opened up my bag of food, and it was crawling with dozens of moths and their larvae! My friends bought some of this food for their hamster and the same thing happened!
My guinea pig fell ill, and a few days later, died. I believe she consumed moth larvae and that's what killed her.