Geckos are a diverse group of small to medium-sized lizards found across nearly every continent except Antarctica. They inhabit environments ranging from arid deserts to dense, humid rainforests. With 2,000 species, their dietary needs vary substantially, but most rely on invertebrate prey. This reliance on insects is key to understanding their diet, particularly concerning common insects like flies.
Geckos and Flies: The Insectivorous Answer
Geckos are overwhelmingly insectivorous; insects form the bulk of their natural diet in the wild. Flies are a common food source for many wild gecko species, especially smaller varieties like house geckos. Geckos are opportunistic hunters that consume almost any invertebrate they can successfully catch. They employ various hunting strategies, from ambush predation to actively chasing targets.
The size and speed of a fly make it a suitable meal for a gecko, particularly smaller insects like mosquitoes or gnats. Geckos use their excellent vision and sticky tongues to secure this fast-moving prey. Eating flies is a normal part of their ecological diet.
Typical Wild Prey and Captive Staple Foods
A wild gecko’s diet is highly varied and depends on local availability and size. Natural prey includes a wide array of invertebrates such as spiders, small beetles, moths, and worms. Larger gecko species may occasionally consume small vertebrates like mice or other reptiles.
In captivity, the diet is structured around staple feeder insects that provide consistent nutrition. Common staples for purely insectivorous species, such as the Leopard Gecko, include crickets, mealworms, and Dubia roaches. These insects are chosen because they are easily bred, readily available, and offer a good nutritional profile.
Dietary requirements change significantly for omnivorous species, like the Crested Gecko and Day Gecko. While they consume insects, these species thrive on commercially prepared powdered diets mixed with water. These diets simulate the fruit, nectar, and pollen that form a substantial part of their natural diet. Feeder insects serve as a supplement, providing additional protein and stimulation.
Feeder insects high in fat, such as waxworms and superworms, are categorized as occasional treats. They offer energy but lack the nutritional balance required for daily consumption. A varied diet of three or more different staple insects, plus supplements, is recommended for optimal health.
Safety and Nutritional Considerations for Feeding Flies
Never feed a pet gecko any insect caught in the wild, including common houseflies. Wild-caught insects pose a substantial health risk due to exposure to pesticides, herbicides, and fertilizers. These toxins can be fatal to a small reptile, even in trace amounts.
The second risk comes from parasites, which wild insects can transmit to a captive gecko. Flies may land on biohazardous surfaces, making them carriers of pathogens or internal parasites like tapeworms. The unknown history of a wild insect means the risk outweighs any perceived benefit.
Flies, even if safely bred, are not suitable as a staple food due to poor nutritional composition. Most insects have an inverted calcium-to-phosphorus (Ca:P) ratio, below the ideal 2:1 required for reptiles. This imbalance can lead to Metabolic Bone Disease if not corrected.
To address this, commercially purchased feeder insects must be “gut-loaded,” meaning they are fed a highly nutritious diet 12 to 48 hours before being offered. Gut-loading ensures the gecko receives the vitamins and minerals contained within the insect’s gut. This process is supplemented by dusting the insects with a calcium and multivitamin powder.
The exception for using flies involves small, commercially bred species like flightless fruit flies (Drosophila), appropriate for hatchlings or very small geckos. Another beneficial option is the Black Soldier Fly Larva (BSFL), which is unique because its Ca:P ratio is naturally balanced, often eliminating the need for calcium dusting. Prioritizing commercially raised, gut-loaded insects is the only safe approach.