Did you know spadefoot toad tadpoles can transform into cannibals when they need to? Spadefoot toads, which are native to North America, often lay their eggs in temporary water puddles. There is always a risk that these puddles could dry up, killing the tadpoles.
As an adaptation to these temporary-puddle conditions, spadefoot toad tadpoles have the ability to switch from an omnivorous form (eating mostly plankton) to a carnivorous form (eating shrimp and other tadpoles, including their own species). You see, when a puddle begins to dry up, the space becomes increasingly crowded, without enough plankton to support the tadpoles. It also becomes really important for the tadpoles to accelerate their development, to become air-breathing adults before the water is gone.
So, a drying puddle triggers biological changes in the tadpoles' bodies. Their heads become larger, with larger, stronger jaw muscles. Their mouths become sharp beaks. Their intestines become shorter (carnivores have shorter intestines compared to herbivores because animal matter is easier to digest than plant matter). They become vicious predators.
This switch to a carnivorous, cannibalistic diet allows the tadpoles to take in more calories, which speeds up their transition into air-breathing adults. Below is a spadefoot tadpole metamorphosing into an adult.
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