which is seen as an adaptation to escape from predators which tries to grasp them by the tail. Tadpoles are typically herbivorous, feeding mostly on algae, including diatoms filtered from the water through the gills. Some species are carnivorous at the tadpole stage, eating insects, smaller tadpoles, and fish. The Cuban tree frog (Osteopilus septentrionalis) is one of a number of species in which the tadpoles can be cannibalistic. Tadpoles that develop legs early may be eaten by the others, so late developers may have better long-term survival prospects. Tadpoles are highly vulnerable to being eaten by fish, newts, predatory diving beetles, and birds, particularly water bird, such as storks and herons and domestic ducks. Some tadpoles, including those of the cane toad (Bufo marinus), are poisonous. The tadpole stage may be as short as a week in explosive breeders or it may last through one or more winters followed by metamorphosis in the spring. Metamorphosis At the end of the tadpole stage, a frog undergoes metamorphosis in which its body makes a sudden transition into the adult form. This metamorphosis typically lasts only 24 hours, and is initiated by production of the hormone thyroxine. This causes different tissues to develop in different ways. The principal changes that take place include the development of the lungs and the disappearance of the gills and gill pouch, making the front legs visible. The lower jaw transforms into the big mandible of the carnivorous adult, and the long, spiral gut of the herbivorous tadpole is replaced by the typical short gut of a predator. Homeostatic feedback control of food intake is largely absent, making tadpoles eat constantly when food is present. But shortly before and during metamorphosis the sensation of hunger is suppressed, and they stop eating while their gut and internal organs are reorganized and prepared for a different diet. Also the gut microbiota changes, from being similar to that of fish to resembling that of amniotes. Exceptions are carnivorous tadpoles like Lepidobatrachus laevis , which has a gut already adapted to a diet similar to that of adults. These continue to eat during metamorphosis. The nervous system becomes adapted for hearing and stereoscopic vision, and for new methods of locomotion and feeding. The eyes are repositioned higher up on the head and the eyelids and associated glands are formed. The eardrum, middle ear, and inner ear are developed. The skin becomes