Growing Food for Amphibians

Introduction. Although rodents and many invertebrates can be purchased from commercial suppliers, shortfalls in distribution can occur during inclement weather, thus many herpetoculturists maintain small colonies of insects and rodents to ensure a steady supply of food for their amphibians. Further details of cultivation of food items are available elsewhere (e.g., Andrews, 1986; Frye, 1991; Jaycox, 1971; Martin et al., 1976; Mason, 1994; Masters, 1975; Mattison, 1982; Obst et al., 1988; Zimmerman, 1986). In addition to the amphibian and reptile literature, tropical fish magazines and other newsletters often have detailed articles about culturing live food items that are suitable for amphibians. Following is brief overview of the culturing of some of the invertebrate species readily maintained in the average home.

It is difficult to estimate how many food item colonies are needed to maintain a collection, but most shortages occur when attempting to rear amphibian metamorphs. In order to avoid shortages, as a general rule one sweaterbox-sized thriving colony of spring-tails should be available for each newly metamorphosed small anuran or salamander. A similar sized colony of white worms should be maintained for slightly larger salamanders.

White worms. The white worm, Enchytraeus albidus, is an annelid worm of the family Enchytraeidae. White worms can be raised in a lidded dark plastic container (e.g., shoebox). Ventilation holes are not required, but if present should be covered with foam or fine mesh screen to prevent infestation with parasitic mites or flies. Moist potting soil and peat moss should fill the container to within a few inches of the top. A quantity of white worms can be introduced to this container. White worms should be cultured at temperatures between 7 and 20°C (45° and 68°F), but do best at the lower end of this range. Oatmeal, white bread that has been soaked in milk or aged tap water, tropical fish food flakes, and vegetables should be placed on top of the soil on a regular basis. Water should be sprayed into the culture as needed to keep soil moist. Feed sparingly and remove food before it spoils.

Red worms. The annelid red worm, Lumbricus rubellus, can be cultured in the manner of the white worm, Enchytraeus albidus, but requires warmer temperatures in the range of 16-20°C (60°-68°F). Burlap or cardboard should be laid on top of the soil to provide hiding spaces. Cricket chow, trout chow, cornmeal, oatmeal, and vegetables should be placed underneath the burlap or cardboard but on top of the soil on a regular basis. Water should be sprayed into the culture as needed to keep soil moist. Feed sparingly and remove food before it spoils.

Springtails. Springtails are tiny primitive insects of the order Collembola that are natural prey items of many amphibians throughout the world. Springtails are easy to culture and the adults rarely exceed 3 mm in length. Springtails can be raised in a lidded, clear plastic container (e.g., shoebox or sweaterbox). Ventilation holes are not required, but if present should be covered with foam or fine mesh screen to prevent infestation with parasitic mites or flies. Moist potting soil free of surfactants, antifungal agents, and fertilizers should fill the container to within 2 inches of the top. A quantity of springtails can be introduced to this container. Springtails can be cultured at temperatures between 20 and 27°C (68° and 80°F). Flaked fish food can be fed on a regular basis and water sprayed into the culture as needed to keep soil moist. It generally takes a month or more for a new colony to produce enough for harvesting. A minimum of one sweater- box-sized colony of springtails should be maintained for each small salamander or anuran. Colonies of springtails have also been maintained on damp gravel with a small amount of moist potting soil at one end of the container.

Flour beetles. Flour beetles, Tribolium spp., are small insects that are relatives of the common mealworm, Tenebrio molitor. Flour beetles are available from many biological supply houses or can be obtained from infested grain items. The generation time and number of eggs produced varies between species of flour beetles, but generally a colony of the confused flour beetle, Tribolium confusum, is thriving within 60 days of founding if maintained at temperatures between 24 and 28°C (75 and 82°F). Flour beetles can be maintained in a lidded, clear plastic container (e.g., shoebox) that is well aerated. Ventilation holes should be plugged with cotton or foam or otherwise screened to prevent invasion by pests such as mites. Excess humidity can quickly kill a flour beetle colony. The substrate can be just the food items used. Commercial cricket diets (not gut-loading diets) can be used to maintain colonies of flour beetles, as can pelleted trout chow, dog food, monkey biscuit, and rodent blocks. The substrate should be kept dry and free of mold. Small wedges of apples or oranges or a moist cotton ball need to be placed within the colony on a daily basis to provide water for the beetles. The fruit or cotton should be placed on a small plastic bottle cap to prevent molding of the substrate. Either adult or larval beetles can be offered as food. New colonies should be started from colonies less than 60 days old.

Mealworms. The common mealworm, Tenebrio molitor, is easily maintained in the average household. The chiti- nous exoskeleton of mealworm larvae limits its use as a food item. Many amphibians swallow their prey whole, and mealworms may appear nearly whole in feces if the exoskeleton was not sufficiently crushed and pierced by the mouth of the amphibian. This problem is not apparent when using newly moulted mealworm larvae, which appear pale white beside the hardened exoskeleton of other larvae. If hard-shelled larvae are to be used, the exoskeleton should be slit with a razor prior to feeding to ensure the penetration of stomach acid and digestive enzymes. The head of the mealworm larvae may also be crushed prior to feeding to minimize the risk of injury to the amphibian’s stomach caused by the mealworm’s escape attempts after ingestion.

There are many possible methods of rearing mealworms, but this author has used the following simple system with great success. Mealworms can be maintained in a lidded, clear plastic container (e.g., sweater-box) that is well aerated. Ventilation holes should be plugged with cotton or foam or otherwise screened to prevent invasion by pests, such as mites. Excess humidity can quickly kill a mealworm colony. Dry sphagnum moss works well as a substrate, and will become finely powdered by the action of the mealworms. Low-fat monkey biscuits (e.g., Zupreem® monkey biscuits) are used as a food source and are constantly available on the surface of the moss. Slices of apple or potato are placed on the surface of the moss and replaced as needed to provide moisture. Additional moss is added as needed. New colonies should be started from colonies that are less than 60 days old.

Fruit flies. Fruit flies (Drosophila melanogaster, D. hiedii) are easily maintained using either commercially available media (Carolina Biological Supply, Burlington, NC) or on homemade media. One formula consists of a volume of 1 part brewer’s yeast to 10 parts instant potato flakes, which is then mixed with an equal volume of dechlorinated water (Waddle, 1996). A mold inhibitor (e.g., tegosept at 4 g/gal water) can be added to the water used for the mix. Wadded paper towels or cotton gauze can be placed into the mix to prevent the media from getting too liquid (from the growth of the fruit fly larvae). Colonies do best if maintained between 24 and 25°C (75 and 77°F), and new colonies are best started from cultures less than 30 days old.