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. 



