v COLOURS OF ANIMALS 351 
showy colours and slow flight. It is good for them to be 
seen and recognised, for then they are never molested ; but 
if they did not differ in form and colouring from other 
butterflies, or if they flew so quickly that their peculiarities 
could not be easily noticed, they would be captured, and 
though not eaten would be maimed or killed. 
As soon as the cause of the peculiarities of these butterflies 
was clearly recognised, it was seen that the same explanation 
applied to many other groups of animals. Thus, bees and 
wasps and other stinging insects are showily and distinctively 
coloured ; many soft and apparently defenceless beetles, and 
many gay-coloured moths, were found to be as nauseous as the 
above-named butterflies ; other beetles, whose hard and glossy 
coats of mail render them unpalatable to insect-eating birds, 
are also sometimes showily coloured; and the same rule was 
found to apply to caterpillars, all the brown and green (or 
protectively coloured species) being greedily eaten by birds, 
while showy kinds which never hide themselves—like those 
of the magpie-, mullein-, and burnet-moths— were utterly 
refused by insectivorous birds, lizards, frogs, and spiders 
(p. 84). Some few analogous examples are found among 
vertebrate animals. I will only mention here a very interest- 
ing case not given in my former work. In his delightful 
book, entitled The Naturalist in Nicaragua, Mr. Belt tells us 
that there is in that country a frog which is very abundant, 
which hops about in the day-time, which never hides him- 
self, and which is gorgeously coloured with red and blue. 
Now frogs are usually green, brown, or earth-coloured, feed 
mostly at night, and are all eaten by snakes and birds. 
Having full faith in the theory of protective and warning 
colours, to which he had himself contributed some valuable 
facts and observations, Mr. Belt felt convinced that this frog 
must be uneatable. He therefore took one home, and threw 
it to his ducks and fowls; but all refused to touch it except 
one young duck, which took the frog in its mouth, but 
dropped it directly, and went about jerking its head as if 
trying to get rid of something nasty. Here the uneatableness 
of the frog was predicted from its colours and habits, and we 
can have no more convincing proof of the truth of a theory 
than such previsions. 
