Frogs arc essentially dependent on vision. They fccd on worms, flies, and
other insects which they catch directly with the mouth or by striking them
with the tongue; for this they use only visual clues. Furthermore, frogs prey
only on moving insects, and their attention is never attracted by stationary
creatures or objects. Nor do they respond with feeding behavior to a large
moving object, instead it provokes an escape reaction. For them, a form
deprived of movement SCClnS to bc behaviorally meaningless. Frogs, then,
appear to recognize their prey and select it for attack from among all other
environmental objects because it exhibits a number of features such as movement,
a certain size, some contrast, and, perhaps, also a certain color. Furthermore,
this ability of frogs to recognize their prey and to snap at it is not altered
by changes in the general environment. Just as wc arc able to read and to
recognize shapes under the most varied conditions, so arc frogs able to scc
their prey and to fccd upon it under the bright light of midday or under the
twilight of morning or evening, whether this bc in their natural environment
or in a small cage in the laboratory.