Formulating a balanced diet for medium to large sized insectivorous reptiles and amphibians poses a unique set of problems. Large insects are difficult to come by in sufficient quantities, and rodents, as we shall see, are often a poor substitute. Canned insects, especially large grasshoppers, offer a convenient and healthful alternative.
Surprising Research on Natural Diets
Many carnivorous reptiles and amphibians prey almost entirely upon invertebrates in the wild, despite being rather large in size. The most extreme example may be found among certain populations of savannah monitors, which eat locusts and snails to the near exclusion of all else.
Even the rapacious marine toad, capable of downing a half-grow rat, falls into this category. In a Herpetologica article published some years ago, stomach analysis of several thousand toads collected in the central llanos country of Venezuela revealed not a single vertebrate prey item…this despite the fact that small rodents, lizards and turtles abound there.
The Problem for Pet Owners
The appetites of a number of commonly kept reptiles and amphibians are difficult (and expensive!) to satisfy with crickets, mealworms and waxworms, leading pet keepers to turn to mice. However, while most largely insectivorous species will take a rodent on occasion in the wild, their digestive systems are not designed to process such food on a regular basis.
Health Problems Related to Improper Diets
Insectivorous herps that are fed a steady diet of rodents often develop health problems, which frequently show up as lipid deposits in the eye, resembling cataracts. Fatal liver and kidney disorders may follow. While cholesterol seems to be the major culprit, intestinal blockages from fur and bone have also been documented.
I have noted these problems, many confirmed by autopsy at the Bronx Zoo, in basilisks, tiger salamanders, Cuban treefrogs and White’s treefrogs. Other species that may fare poorly on rodent-based diets include smaller monitors (i.e. black tree and Merten’s water monitors), American and African bullfrogs, frilled dragons, marine and Colorado River toads and horned frogs.
Canned grasshoppers, offered via tongs, provide an ideal solution to this dilemma. The grasshoppers selected for canning are large enough to satisfy hearty appetites, nutritionally sound, easy to coat with powdered supplements and captive raised to avoid pesticide-related concerns. Zoo Med supplies large, wingless grasshoppers, while Exo Terra’s grasshoppers are winged. Wingless grasshoppers are best for medium-sized pets, such as White’s treefrogs.
Canned grasshoppers are also relished by many turtles (i.e. box, wood, snapping, Australian snake-necked), sugar gliders, flying squirrels, hedgehogs, hill mynas, emperor scorpions, tarantulas and other pets with carnivorous leanings. Oscars, peacock bass and other large aquarium fishes love them…and they make great fishing bait!
Other Large Invertebrates
Culturing roaches and collecting cicadas are also useful options for owners of large insectivorous pets. Please see my articles The Orange Spotted Roach and Cicadas for details. For information on other types of canned invertebrates, please see Canned Insects and Other Invertebrates.
Crayfishes are an ideal, high calcium food for many large herps. Where legal, they can be caught by trap, seine or hand line (this last is actually great fun, and has resulted in a few “trophy-sized” catches for me!).
The summary of an interesting experiment dealing with the effects of a high cholesterol diet on Cuban treefrogs is posted at http://www.bioone.org/doi/abs/10.1638/1042-7260%282001%29032%5B0305%3ACLDICT%5D2.0.CO%3B2?journalCode=zamd.