 Newly hatched New Guinea crocodiles feed on aquatic insects , spiders , tadpoles , freshwater snails , frogs , fish and small mammals . As they grow , so does the size of their prey and their consumption of fish rises , but they still will eat anything of a worthwhile size that they can find . An adult 's diet is largely fish , caught by sweeping the snout sideways and snapping at the prey , but also includes shrimps , crabs , frogs , snakes , birds and medium @-@ sized mammals . A crocodile catches its prey by stealth with a flick of its head , impaling it with its sharp teeth and gripping and crushing it . The jaws cannot move sideways to chew the food ; instead , the crocodile 's head is tossed to move the prey to the back of the mouth before the prey is swallowed whole . This crocodile is surprisingly agile and can lunge its body upward into the air to catch bats , flying birds , and leaping fish . It can also probe into the mud at the bottom of river or swamp with its snout to search for crabs and molluscs . 
