Rats, including the common Norway rat (Rattus norvegicus) and the Roof rat (Rattus rattus), are highly adaptable, opportunistic feeders. Rats can and will eat flies, but insects are not a primary part of their regular diet. They consume virtually any available food source to meet their nutritional needs. While rats rarely expend energy hunting adult, flying insects, they frequently consume flies in their immobile stages.
Opportunistic Omnivores: A Rat’s General Diet
Rats are classified as opportunistic omnivores, meaning their diet is extremely varied and depends on what is most readily available. Given a choice, both Norway and Roof rats prefer a diet rich in carbohydrates and fats. Norway rats favor meat, grains, seeds, and human refuse, typically feeding in one or two spots. Roof rats often display a more vegetarian preference, consuming fruits, nuts, seeds, and vegetables, and taking small meals at multiple locations.
The foundational diet for rats in the wild is largely plant-based, consisting of seeds, fruits, and grains. Their omnivorous nature allows them to consume a wide range of other items, including small vertebrates, eggs, and fungi. Because rats have a high metabolism, they must constantly feed. This necessity pushes them to explore and exploit every potential food source, including insects, allowing them to thrive in diverse habitats.
Insects as a Necessary Protein Source
Insects, including flies and their larvae, serve a significant nutritional purpose for rats, providing essential protein and fat. When preferred food sources like grains or produce become scarce, insects act as a valuable supplement to prevent malnutrition. Insect-based meals offer a high-quality source of protein, rich in essential amino acids.
The protein quality of insects is comparable to other animal protein sources. This makes them a nutrient-dense option, important for growth and reproduction in wild rat populations. Insects provide necessary micronutrients and fatty acids that a purely plant-based diet might lack, ensuring a more balanced nutritional profile.
Active Hunting Versus Scavenging
The consumption of flies by rats is most often a result of scavenging rather than active hunting of flying adults. Adult flies are quick and agile, making them difficult targets, though rats may catch slow-moving insects like moths. The primary way flies enter a rat’s diet is through consuming their larval stage, commonly known as maggots.
Maggots are fly larvae attracted to and feeding on decaying organic matter, including carrion and garbage. When a rat feeds on a discarded food source or a carcass, it inadvertently consumes the maggots present within the material. This provides a substantial, immobile, and easily accessible source of protein without the energy expenditure of a chase. The larval forms found in refuse contribute the most fly-related protein to the rat’s diet.