Color and Pattern and their Uses 
605 
Exactly such an explanation of brilliant color and contrasting markings 
is afforded by the theory of warning colors. It has been conclusively shown, 
by observation and experiment, by several naturalists,* that' many insects 
are distasteful to birds, lizards, and other predaceous enemies of the insect 
class. 
The blood-lymph or some specially secreted body fluid of these insects 
contains an acrid or ill-tasting substance so that birds will not, if they can 
recognize the kind of insect, make any attempt to catch or eat them. This 
letting alone is undoubtedly the result of previously made trials, that is, has 
been learned. Now it would obviously be of advantage to those species of 
insects that are ill-tasting if their coloring and pattern were so distinctive 
and conspicuous as to make them readily learned by birds, and once learned 
Fig. 791. —Larva of the monarch butterfly, Anosia plexippus , conspicuously marked with 
black and whitish yellow rings, and distasteful to birds. (Natural size.) 
easily seen. A distasteful caterpillar needs to advertise its unpalatability so 
effectively that the swooping bird will recognize it before making that single 
sharp cutting stroke or peck that would be about as fatal to a caterpillar 
as being wholly eaten. Hence the need and the utility of warning colors. 
And indeed the distasteful insects as far as recognized are mostly of con¬ 
spicuous color and pattern. 
Such warning colors are presumably possessed not only by unpalatable 
insects, but also by many that have certain special means of defence. The 
wasps and bees, provided with stings, dangerous to most of their enemies, 
are almost all conspicuously marked with yellow and black. Many bugs, 
well defended by sharp beaks, possess conspicuous color-patterns. 
Terrifying appearances.—Certain other insects which are without special 
means of defence and are not at all formidable or dangerous are yet so marked 
or shaped and so behave as to present a curiously threatening or terrifying 
appearance. The large green caterpillars of the sphinx-moths have a curious 
rearing-up habit which seems to simulate threatened attack (Fig. 792). 
They have, too, a great pointed spine or horn on the back of the posterior 
* A most interesting recent account of a long series of such observations and experi¬ 
ments is presented in “The Bionomics of South African Insects,” by G. K. Marshall 
and E. B. Poulton, Trans. Ent. Soc. Lond., 1902. This paper contains the records of 
five years of careful study in the field of the phenomena relating to the theories of warning 
colors and mimicry. 
