protective: habits. 255 



so slight that it is hardly worthy of consideration. After a long acquaintance 

 with these beetles, both in the tropics and in the temperate regions, it seems 

 to me that the habit is no more than the response produced by excessive fear. 

 There can not be the slightest doubt that fear is a psychic phenomenon which 

 is found in all animals and may be aroused by quite varied stimuli. In the 

 higher animals the continued application of a stimulus that excites fear pro- 

 duces a condition of muscle tension and inability to move, and frequently a 

 state of complete unconsciousness, while in the human race these states are 

 always accompanied by characteristic outward signs — pallor, trembling, pro- 

 trusion of the eyeballs, clenched fists, tense muscles, and other characters. 



If a slight noise be made with a tuning fork these beetles pause and assume 

 the pose described ; if the noise be continued they seek safety in flight ; and 

 then, if it be greatly increased, they assume the so-called death attitude, from 

 which they emerge only after the stimulus has passed away and sufficient time 

 has elapsed for the beetles to recover from their fright. The attitude assumed 

 while in this state is caused simply by the nervous shock received by the body 

 of the beetle, and especially by the muscular system, the reaction differing in 

 no way from the well-known effects upon the muscular system of similar 

 states in the human subject. Therefore, until more conclusive evidence is 

 produced to show that the habit has the high utility so often attributed to 

 it, death-feigning must be regarded as the specific response to continued or 

 excessive fear-producing stimuli. In these beetles the habit is, I should judge, 

 quite as frequently productive of ill results as of beneficial ones. I am of the 

 same opinion as Morgan, that ''the origin of these trophisms can not be ac- 

 counted for on the ground of their benefit to the individual or the race." Cer- 

 tain it is that in Leptinotarsa there is not the slightest evidence that this habit 

 has any selective value, or that it is of any constant or marked utility to the 

 race. It m^ay occasionally be of use in the preservation of an individual 

 beetle, but such rare and sporadic utility of the habit would not bring it under 

 the operation of natural selection, and I can not conceive of any rational way 

 in which it would have been produced by this agency. On superficial exam- 

 ination or on first sight this habit would appear to be one of great value to the 

 species, but a better understanding of the conditions of life in the species and 

 of the relation of enemies thereto shows clearly that the habit is really of little 

 utility in the life and death struggle of the species, and, therefore, has an ex- 

 tremely low selectional value, if any at all. For the purposes of this research, 

 however, it is a useful character in that it is inherited in its full intensity and 

 has a manner of outward manifestation that is more or less characteristic for 

 each species. Moreover, when a new species arises, the habit may also be 

 modified at the same time, which shows conclusively that not only are the 

 most superficial structures, such as color and ornamentation, able to make 

 rapid developments in their evolution, but that instincts and deep-seated 

 nervous reactions can also change as quickly and easily as do the supposedly 



