252 HABITS AND INSTINCTS IN IvKPTlNOTARSA. 



exactly with the standard of the race are able to survive in any numbers. 

 That is, here natural selection eliminates, and not perpetuates, the extremes 

 of variation. It is a self-evident fact that the major portion of any species 

 numerically strong must be well adapted to its conditions of existence, and 

 these beetles are no exception to the rule. In these beetles, however, we find 

 that the selective action of assortive mating and hibernation, both of which 

 are strong and important selective agents, tend in the direction of segregation 

 and an elimination of the individuals farthest removed from the standard of 

 the race. This conservative or segregational selection has been an important 

 factor in the evolution of the genus Leptinotarsa, and also in evolution in 

 general. 



HABITS AND INSTINCTS CONNECTED WITH SELF-PRESERVATION. 



The devices exhibited by these beetles in one way or another, which enable 

 them to obtain a measure of immunity from the attacks of their enemies, have 

 already been examined in a preceding chapter. These have been found to be 

 largely bright colors which, accompanied by the exposed situation in which 

 the beetles live, make them conspicuous objects upon their food plants, and 

 thus serve to advertise the inedibility of the possessors thereof. These warn- 

 ing colors do not entirely protect the beetles from their enemies, because we 

 find that each generation of enemies has to be educated, and in this education 

 a small percentage of the insects are killed. The influence of warning colora- 

 tion, however, is purely passive ; yet there are in this genus habits that are 

 active agents of protection, and that are brought into play only on the ap- 

 proach of danger. It is these which will now be considered. 



The most widely distributed protective habit shown by animals on the ap- 

 proach of danger is that of assuming a perfectly motionless position, with all 

 the organs and appendages as closely drawn together as is possible. Observa- 

 tions upon habits of this kind have frequently been made upon birds and mam- 

 mals, but less frequently upon lower forms. Many insects have this habit as 

 fully developed and display it in the same manner as do the higher classes of 

 animals. In the genus Leptinotarsa it appears to a greater or less extent, 

 most frequently when the food plant is shaken or there is a sudden noise 

 or a shadow passes quickly across the beetles. Oblongata and signaticollis 

 respond to these stimuli, which are unusual in the habitat, by stopping quite 

 still wherever they are and drawing the legs and antennae as close to the body 

 as is possible. In this perfectly motionless position they are far less easily 

 seen than they are when moving. The length of time during which this pose 

 continues depends upon the nature of the stimulus and its duration. If it is a 

 passing shadow which is not repeated, the beetle within a few seconds goes 

 on with its activities, whereas if the shadow passes back and forth over the 

 beetle repeatedly it remains in this pose for some minutes, and if the stimulus 



