Growing tadpoles and watching them go through metamorphosis is a fun and exciting science activity for children. Most tadpoles are herbivores and do well when fed fish flakes or boiled lettuce. Once tadpoles turn into small frogs, or froglets, however, they require a different type of diet.
The digestive tract of a tadpole, like most other herbivores, is long to allow for proper digestion of coarse plant matter. During metamorphosis as the legs and lungs are developing, the digestive system is also transforming into a shorter tract more similar to omnivores and carnivores. Upon metamorphosis, this transformation is complete and frogs undergo a major dietary shift from plant to animal matter.
Terrestrial froglet diet
Newly transformed froglets do best when given a diet of small insects (e.g., fruit flies) or worms. Keeping a population of insects tiny enough to be consumed by a froglet is difficult. Froglets may eat a half a dozen flies daily, and purchasing only a few is not often cost-effective or feasible. Therefore, maintaining a colony of insects to be used as froglet food is a good idea.
Wax worms can be fed to a froglet and can be harvested when at small sizes. However, a diet of wax worms alone may leave a froglet malnourished so combining these worms with another food source (e.g., ants, woodlice, springtails) is best.
Many pet stores sell pinhead crickets that may be small enough to for a newly transformed froglet. As with all food sources, it is important to make sure they are actually small enough to be consumed. If they cannot fit into your froglet's mouth, you will need to find a smaller food source. It may also be necessary to expose the froglet to natural sunlight to stimulate vitamin D production, or sprinkle its food with a supplement, otherwise it may develop rickets.
Aquatic froglet diet
An exception to the rule of feeding insects to froglets occurs in the African Clawed Frog (Xenopus laevis or Xenopus tropicalis). This species is fully aquatic (they live through both tadpole and adult frog stages in water) and does not require insects or small animals once metamorphosis is complete.
The African Clawed Frog is the species of frog sold in many pet stores and in science kits used to study metamorphosis. You can feed African Clawed Froglets commercially-available pellets (e.g., Frog Brittle), fish pellets or pieces of raw meat. This species is not discriminatory with respect to diet, and it can thrive on many types of food.