Dr. Nancy Anderson
Carnivorous reptiles are the easiest reptiles for which to provide complete and balanced diets. Most wild carnivorous reptiles eat whole animals, usually rodents or small birds, which are readily supplied in captivity. Fewer nutritional deficiencies or excesses are seen in this group of reptiles than any other if they are fed whole prey. In fact, animals mistakenly fed animals parts – that is all muscle or liver – suffer severe nutritional disease.
Reptiles should be fed frozen and THAWED (to 100 degrees Fahrenheit) or freshly killed prey animals. The most effective means of thawing frozen prey is to seal the food item in a zip lock bag, and then place the bag in water just warmer than the prey animal's normal body temperature. Once the food is completely thawed, it can be presented to the reptile.
Many snakes are able to detect very small temperature differences, so feeding thawed prey items at the appropriate temperature should stimulate some reluctant feeders to eat. In addition, placing the prey in plastic bags, keeps the texture of the surface of the animal closer to that of a live animal since it is not wet. The plastic bag also prevents the prey animal from picking up odors from the soak water.
Feeding of live vertebrate prey (animals with back bones) increases chance of serious injury to the reptile and is not recommended. Food animals can be fed; they should be raised on excellent diets, as the reptile will only receive its nutrients through the animal. Supplements for reptiles eating vertebrate prey are usually not recommended. Offering obese prey animals may cause steatitis (a disease that causes inflammation of the fat pads).
Some carnivores such as king snakes prefer or will only eat other snakes. It is extremely important to ensure that these feeder snakes are free from disease and parasites. If the reptile will feed on thawed, frozen prey, it is recommended to freeze all feeder snakes for at least 30 days prior to feeding as a precaution against transmission of parasites. Good quality feeder snakes can be difficult to obtain.
Some snake eaters can be fed mice stuffed into a shed snake skin. Some carnivores will eat only amphibians or small reptiles. Prevention of disease transmission is extremely important. Some amphibian eaters can be trained to eat mice by placing a mouse inside a fresh frog skin or smearing a mouse with frog slime. Be careful not to attempt to feed amphibians with toxic skin secretions.
Some snakes and monitors eat mostly eggs. Ideally these eggs should be fertilized and contain embryos at different stages of development. Reptiles fed only unfertilized hen eggs suffer many nutritional deficiencies.
Some aquatic reptiles eat fish exclusively. Other reptiles eat fish if given the opportunity. Frozen fish may need to be supplemented with thiamine and vitamin E, especially smelt and other fatty fish. Aquatic animals should be fed in a separate tank.
Some reptiles only eat crustaceans, gastropods, worms or other specialized diets. Special attention needs to be paid to the natural history of reptiles needing specialized diets. If the suitable prey items cannot be obtained YEAR ROUND, the animal should not be kept in captivity.
Nutritional diseases such as secondary hyperparathyroidism are common in crocodilians because many owners feed their pets only hamburger or table scraps. Feeding complete animal diets like whole fish, rats, chickens or rabbits prevents nutritional diseases. Crocodilians often exhibit feeding frenzy and cage mate trauma is common. They should be fed individually whenever possible.
Most food insects fed in captivity are deficient in nutrients. These nutrients can be supplemented by providing an excellent diet for the insects aimed at maximizing their nutritional worth and also aimed at providing extra nutrients to the reptile via intestinal contents of the insect. Crickets, mealworms, wax worms, and inch worms are commonly fed to reptiles. It is important to raise them on a high calcium medium such as chicken layer mash or special diets formulated to feed crickets used to feed reptiles; stick with well known brands. Even so, dusting the crickets and mealworms with vitamins and calcium is recommended. The vitamin supplement needs to contain vitamin D3 (not D1 or D2). Ideally, the calcium supplement should NOT contain additional vitamin D or phosphorus, which often shows up as phosphate on the label. Adding too much vitamin D causes calcification of soft tissues and too much phosphorus causes soft bones.
An ideal calcium source is calcium carbonate or calcium combined with a sugar. Immature and reproductively active insectivores should receive dusted insects 3 to 5 times per week. Males and non-reproductive females should received dusted insects 1 to 2 times per week.
If large enough, insectivores may take pinkie mice or earthworms as an additional source of nutrients. Juvenile crickets and mealworms are excellent to feed to small or neonatal insectivores because of their small size and lack of chitin. Wingless fruit flies are another good source of food for small insectivores. Some insectivores, such as the horned lizard that only eats certain species of ants, require specialized diets that are difficult or impossible to provide in captivity. Do not purchase or collect these animals from the wild to be pets unless you can consistently provide an adequate diet. Otherwise, they will slowly die from starvation.