140 ZOOLOGY. 



(ichneumons, birds, etc.). Only a few of them die, 

 therefore, if the weather is favourable. As a result of 

 this, the July butterflies and the eggs laid by them are 

 relatively numerous, so that the number of caterpillars 

 appearing in late summer may be very large. These 

 caterpillars, however, live almost exclusively on^ the 

 various kinds of cabbage and kohl rabi, and it is 

 this second generation which in many years is so 

 harmful. At the beginning of August the caterpillars 

 are ready to become pupae, and for this purpose they 

 seek tree stems, hedges, walls, etc. The pupae now 

 formed live as such through the winter. During this 

 period, however, they are exposed to many dangers 

 (damp, cold, sudden alternation between very low and 

 very high temperatures ; ichneumons, birds), and 

 most of them perish, so that only a few butterflies 

 come out the following spring, and lay but a few 

 eggs. It is therefore obvious that the flrst generation 

 of caterpillars (May, June) is much less numerous 

 than the second generation occurring from late summer 

 to autumn. Under exceptionally favourable con- 

 ditions even a third generation may appear, since 

 caterpillars of the second generation are able to 

 become pupae at the beginning of August ; and these 

 pupae, instead of remaining as such over winter, 

 become butterflies the same month. These, again, 

 lay eggs from which the caterpillars of the third 

 generation are hatched, which, however, are not 

 always fully developed before the advent of the cold 

 weather, and in this case perish. It is clear that, in 

 the case of pupae which develop into butterflies during 

 August in about fourteen days, the unfavourable 

 influences have either no eflect (unfavourable weather) 

 or but little (ichneumons, birds), so that the butterflies 

 appear in flocks, which wander into other regions, 

 since they have themselves, when larvae, devoured the 

 cabbage and turnip plants. In reference to the 

 damage ett'ected by the caterpillar, it may be observed 



