A hamster in captivity can occasionally eat mealworms or earthworms, which have high protein contents. Boiled egg whites and small pieces of clean, cooked chicken are also sources of extra protein. They can also eat wheat grain, sunflower seeds, and locusts. The teeth of Campbell's dwarf hamster never stop growing. Like all rodents, they must, therefore, gnaw regularly to keep their incisors from growing into the skin of the mouth and causing pain and irritation. Smooth, young wood from nontoxic trees, such as apple and willow, is readily used by most species in the genus. Most pet stores sell nontoxic wooden chews designed for rodents in captivity.