Yellow mealworm beetle (Tenebrio molitor) feeding on rolled oats. These beetles are a species of darkling beetle and reach lengths of 2.5 cm. They are scavengers and eat decaying leaves, dead insects and feces. They are also known to infest stored grain supplies. They prefer living under rocks and logs and are found in temperate regions worldwide. Their larvae, referred to as mealworms, are typically used as a food source for reptiles, fish and birds.