If it gets too cold at night, the food may rot inside the stomach, like the other poster have mentioned. I usually feed them salad early in the morning or early afternoon. This way they have all day to bask and digest their food properly, getting the nutrients that they need. Salad is a bit difficult to digest compared to live prey items and it takes all day to digest them properly. Plant have what you called cellulose for cell walls to protect them from predators that might eat them. Plant eaters have microbes inside their stomach to help them breakdown plant tough cell walls so the digestive juices can get in their and digest it; however, to digest them properly they need good amount of heat because the microbes function better at certain temperature. If it gets too cold, it may not be able to properly breakdown the plant matters.
