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The diets that you provide your reptile and amphibian pets are of critical importance in maintaining their good health and longevity. Providing a balanced diet can be a quite simple matter for some species and, unfortunately, nearly impossible to achieve with others. Proper nutrition plays an important role in every aspect of your pet’s life, from its ability to grow normally and reproduce to less obvious areas, such as the functioning of its immune system. Reptile and amphibian hobbyists today have a wide variety of both prepared and live foods from which to choose when formulating a diet. In most cases, this is a very good state of affairs. However, sometimes it has a tendency to make us a bit lazy -- for example, is very easy to provide an insectivorous lizard with a diet based on one or two readily available food items when, in actuality, the animal may need a great deal more variety to maintain optimum health.
What I would like to do in this article is to present some general principles and ideas for your consideration. Please bear in mind that actual feeding techniques - how to present the food -- will also affect the ultimate value of the diet that you provide. For example, the length of time between a food animal’s introduction into the terrarium and when it is actually eaten will affect how much of its vitamin/mineral supplement coating will be passed along to your pet. Whether food insects will live or die within the terrarium, and how to keep track of the food intake of secretive or nocturnal pets will also affect the manner in which you must present the food. All of these factors, and many more, will be addressed in future articles. Until then, please contact me with your questions and observations on this subject.
There are two basic approaches to feeding reptiles and amphibians in captivity. One method is to identify one or two commercially prepared diets that provide all of the nutrition that your pet needs for a long and healthy life. This option is available to those who keep animals, such as tortoises and newts, that normally consume, or will accept, non-living food items. Animals that consume live prey in the wild will generally need a varied diet in captivity (one notable exception is most of the commonly kept snakes, all of which do quite well on a diet composed entirely of rats and mice).
In my experience, trout chow, designed for use in trout hatcheries, provides many of the nutrients required for the growth and reproduction of aquatic amphibians such as the Mexican axolotl, Ambystoma mexicanum, the African clawed frog, Xenopus laevis, the ribbed newt, Pleurodeles waltl, and related species. Another very good option is Reptomin floating food sticks. I have raised Mexican axolotls over several generations on a diet comprised of 50% trout chow, switching to 90% as the animals matured (the balance of the diet was made up of black worms, minnows, earthworms and crickets). Adults bred yearly on this diet, and lived to age 15-17 years. Carnivorous aquatic turtles, such as the musk turtle, Sternotherus odoratus, do well on a diet composed mainly of commercial turtle chow or trout chow, but with these animals it is also important to provide ample amounts of whole fish, insects and earthworms and, depending upon the species, fresh greens. Goldfish are fine to use on an occasional basis, but please do not use them as the sole food source for any animal, as such has been implicated in liver damage and other problems in a number of species. Minnows and shiners are a much better alternative - largely raised in semi-natural outdoor ponds, these fish feed upon a variety of insect prey as well as the commercial food given to them, and provide a better source of nutrition than do goldfish.
A number of other theoretically complete diets are now available for bearded dragons, green iguanas, tortoises, box turtles and other reptiles. Most of these have been formulated with a great deal of care and after extensive research. Until long-term test results are available however, I would suggest using these as 25-50% your pet’s diet, with the rest being made up of a variety of foods that the animal would normally consume in the wild.
Most of the commonly-kept snake species do well on a diet consisting of but one or two types of food animal (mice, rats, rabbits, etc.). In fact, some years ago, some hobbyists experimented with vitamin/mineral supplement-coated rodents as snake food. The results were quite distressing -- in a few cases the snakes became rigid and unable to move after time, while in others they expired. I am not sure if the reasons were ever determined by autopsy, but I suspect over-calcification as the culprit. Certain snakes – green anacondas, Eunectes murinus, are notorious in this regard - seem to become "fixated" on one food item and will refuse all others. This occurs most often with wild-caught individuals that may have been hunting animals that smell and taste very differently than those you are able to provide. One large (16 foot) anaconda formerly under my care at the Bronx Zoo refused laboratory rats but eagerly consumed rats that I trapped in the surrounding neighborhood (the lab and wild rats are the same species - the Norway rat, Rattus norvegicus). Another, over a course of many years, would eat only muskrats while its cage-mate accepted only ducks.
In many cases, such finicky eaters can be induced to accept new foods by “scenting” them with their favorite prey. This is accomplished by rubbing the new food item with the favorite or, in some cases, by placing a bit of the preferred food in the mouth of the new food. Even snakes that are confirmed food specialists, such as the king cobra, Ophiophagus hannah (obviously not an animal that should ever be considered as a pet!), which in the wild feeds mainly upon other snakes and the Eastern hog-nosed snake, Heterodon platirhinos, which prefers toads, can be tricked in this manner. Of course, such “food-switching” should only be done if the food item provided as an alternative supplies the animal with adequate nutrition. In the cases mentioned above, both species lived well and reproduced on diets comprised of mice and rats (Note: a bit of cooking skill is often required of zoo keepers working with king cobras, as certain individuals can only be tricked into accepting rats by boiling a bit of a dead snake, retained for this purpose, in water and then pouring a mixture over a rat). Pisciviorous, or fish-eating snakes, such as the banded water snake, Nerodia sipedon, seem to require a bit more dietary variety than do their rodent-eating relatives. But even with such animals, merely alternating the species of fish offered is enough to maintain their good health. Insectivorous snakes are not common in the pet trade, but those of you who keep them should attempt to provide as much dietary variety as possible. Smooth green snakes,Ophiodrys vernalis, for example, rarely thrive on a diet comprised solely of crickets, but do quite well if offered caterpillars (a special favorite), spiders, grasshoppers and other invertebrates. Interestingly, and in contrast to most snakes, green snakes and related species also seem to require a source of UVB light as well. Ringneck snakes, Diadophis punctatus and DeKay’s (brown) snakes, Storeria dekayi, favor slugs, but should also be offered wax worms, crickets, spiders, small earthworms and the like.
Insect-eating lizards, frogs and salamanders fare much better in captivity if offered a wide variety of insects and other invertebrates as food. Field studies show that many species consume quite a large range of prey in the wild. I can recall watching marine toads, Bufo (Rhinella) marinus each evening at supper during my time in Costa Rica. A group of 5-6 toads gathered at the kitchen door each night, drawn by the insects that clustered about the light there. Even through mere casual observation I was able to see that the toads consumed no less than two dozen different types of insects (being one of the very few Anurans that will take non-living food, the toads also ate dog food – the largest of them pushing open the screen door to get at it!). Studies of free-living reptiles and amphibians also reveal that their diets may vary greatly throughout the year. Some populations of savanna monitor lizards, Varanus exanthimaticus, for example, consume only snails or locusts for three to four months of the year, due to the ready availability of such animals at those times. In forested areas of the Eastern United States, Eastern box turtles, Terrepene carolina, wood turtles, Clemmys insculpta and even copperhead snakes, Agkistrodon contortrix (again, obviously, an animal that should never be considered as a pet) gorge themselves on the huge numbers of cicadas that die and fall to the ground at summer’s end. Such factors may or may not affect the long-term health of these species in captivity, but they should be borne in mind. I would greatly appreciate feedback from any readers who have had experience or interesting observations in this area. Collecting invertebrates, fish and other creatures as a means of adding variety to your pets’ diets is a very useful and interesting option. You can also increase a food animal’s nutritional value by feeding the animal itself a healthful diet before offering it to your pet. I will explore these ideas further in future articles, but in the meantime please pass along your thoughts and observations to me.
To Supplement, Or Not?
Sometimes, either due to lack of opportunity or to the type of animal involved, it is nearly impossible to provide a varied diet to an insectivorous reptile or amphibian. In these cases we must rely upon commercially available supplements to hopefully provide the nutrients absent from a limited diet. The topic of food supplementation is a quite complex one, and I will write more about it in the future. For now, please bear in mind that powdered food supplements should not be indiscriminately used but must be considered on an individual basis. For example, a pet adult American bullfrog, Lithobates (Rana) catesbeiana, being fed earthworms, crayfish, minnows, roaches, crickets, wild-caught insects and an occasional pink mouse would likely need no supplementation at all (beware: these robust fellows will happily swallow near same-sized tank-mates as well!). However a green-and black dart poison frog, Dendrobates auratus, whose diet consists of only fruit flies and tiny crickets, should be given a vitamin/mineral supplement with up to two thirds of its meals. In all cases, growing and gravid animals need greater quantities of vitamins and minerals than do adults.
You Can Help
The nutritional requirements of captive reptiles and amphibians are still relatively unstudied. This is, therefore, an area in which observant hobbyists can make great contributions. Much of what I have learned over the years has come from my conversations with dedicated pet keepers and through my own tinkering and experimentation. What you learn can be of great value, not only to other hobbyists, but also to the zoo community and to the survival of those many species that are now in grave danger in the wild state. I would be most pleased to hear from you on this subject. I can also advise you on ways of communicating your observations to professional herpetologists and to the zoo community in general. Please remember that even the most renowned biologists started out as did you -- someone interested in keeping and observing animals. There is so much for us to learn in this area that even what may seem the simplest of observations can be very important. Please record your thoughts and pass them along to me at every opportunity.
Thanks very much. Until next time, Frank Indiviglio.