THE UTILITY OF THE COLOR-PATTERN. 9 



THE UTILITY OF THE COLOR-PATTERN. 



The utility of the color-pattern is obviously not that of protective resem- 

 blance, for it is decidedly conspicuous in the green surroundings which the 

 beetles frequent. This conspicuousness is generally thought to be expli- 

 cable as a result of the habit these beetles have when disturbed of expel- 

 ling a disagreeable fluid from the ends of the femora. The possession 

 of a striking and peculiar appearance, by which the bird or other pre- 

 daceous animal might associate this painful experience, would obviously 

 be advantageous. In Poulton's terminology the color is aposematic. The 

 only other explanation that seems at all plausible is that of sexual attrac- 

 tiveness, i. e., the color is epigamic. The apparent indifference with which 

 Hippodamia convergens, spotted or unspotted, breed together at Berkeley, 

 California, although both forms are common there, makes this unlikely. 

 I collected a number of mating pairs and could see no evidence for either 

 assortative or preferential mating, in this confirming Kellogg, who also 

 collected a number of mating pairs and reached the same conclusion. 



The explanation of the ground-color of these beetles as warning or apo- 

 sematic may be accepted upon the following evidence from Judd (1899), 

 based upon extensive examinations of the stomachs of birds: 



In the Coccinellidas we have showy insects, ill-scented or flavored, that are eaten by 

 but very few birds the flycatchers and swallows ; and hence here is a whole family 

 which conforms well with the theory of warning coloration. * * * The showy, ill- 

 flavored Coccinellidae [are] * * * almost as * * * highly protected from birds 

 as the hairy caterpillars and the elm leaf-beetle. 



To this may be added my attempt to feed Coccinella novemnotata to a 

 catbird reared in captivity. The bird took the beetle up to its perch, but 

 then dropped it. The beetle walked away without further molestation. 



Since Judd finds that the barred and spotless species as well as the 

 spotted species are protected, the particular patterns can be of little im- 

 portance, although they are so diverse. In flight, where the beetles are 

 most attacked, the pattern is inconspicuous, while the ground-color is evi- 

 dent. But what is quite conclusive is the origin and persistence of varieties 

 having fundamental differences from the pattern of the spots of the par- 

 ent species. The fundamental usefulness of an aposematic pattern would 

 depend, above all, upon its constancy. If the spotted pattern, which is 

 so widespread in the family and is the primitive pattern for many genera 

 or subgenera, has a strong association value with distastefulness, all 

 departures from it would be suicidal; yet we find they are not. It is 

 certain, then, that there is no high selective value in the spotted pattern, 

 but it is possible that there is a feeble one. The loss of the spots or their 

 change into other patterns must, then, be the result of some stronger 

 evolutionary force, which I believe to be determinate evolution, over- 

 coming the slight advantage placed on spottedness by natural selection. 



