Eyesight of Birds 
It would therefore seem that all these elaborate 
“protective ” devices are unnecessary refinements 
if regarded as a protection against invertebrate, 
reptilian, and amphibian foes. Birds, on the other 
hand, appear to have exceedingly sharp eyesight, 
so that in order to deceive them the resemblance 
requires to be very close. Indeed, as regards 
those birds which systematically hunt for their 
prey among leaves and grass, it seems doubtful 
whether the alleged “protective” resemblances of 
caterpillars to twigs, etc.,are sufficient to be of much 
use to them. Thus Beddard writes (on page 91 
of Animal Colouratin): “Judging of birds by 
our own standard—which is the way in which 
nearly all the problems relating to colour have 
been approached—does it seem likely that we 
should fail to see a caterpillar, perhaps as long 
or longer than the arm, of an obviously different 
texture from the branches, and displaying in 
many cases through its semi-transparent skin the 
pulsation of the heart, for which we were par- 
ticularly searching?” 
Now, birds certainly feed very largely on 
caterpillars, while they are but rarely seen to eat 
butterflies. If, therefore, the aim and object of 
these special resemblances is the protection of 
the species, we should expect to see them in a 
nearly perfect state in caterpillars on which 
birds feed very largely, and poorly developed in 
butterflies, which do not appear to be greatly 
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