50 BULLETIN 15 7, U. S. NATIONAL MUSEUM 



On the next day (September 17) the meadows were again visited 

 in order to observe the effect, if any, on the butterflies. It was at 

 once evident that the milkweed butterfly had enormously increased 

 in numbers, and also that those present were without exception 

 quite fresh. Furthermore, by far the greater part of those captured 

 were males. A visit on the following day (September 18) showed 

 this butterfly to be still more numerous, outnumbering all the other 

 kinds of butterflies taken together, while of those captured a slight 

 majority were fresh females. 



From the very great increase in the numbers of the male milk- 

 weed butterflies on the day following the shower, and of the females 

 on the succeeding day, it would seem evident that the moisture pro- 

 vided by the shower had enabled many of these insects, prevented 

 from emerging by the dryness, to escape from the chrysalids. In 

 the case of this species the sudden increase in the numbers of indi- 

 viduals could not have been due to the normal appearance of a late 

 brood, as the emergence of the late-summer brood normally takes 

 place gradually over a period of several weeks' duration, and the 

 males and females remain throughout that time in the same relative 

 proportion — occurring in practically equal numbers. It was un- 

 doubtedl}'' the result of the simultaneous appearance of individuals 

 which normally would have emerged over an extended period and, 

 had there been no rain, would have died in the pupal stage. 



I can not find that the sudden appearance of the milkweed but- 

 terfly in great numbers after storms has previously been recorded. 

 But the name by which this insect is commonly known in certain 

 country districts — storm fritillary — would suggest that it has been 

 noticed. 



Of the other species in the meadows, Eureina lisa was the only one 

 that became appreciably more numerous immediately after the 

 storm. For the next few days all the individuals of this species 

 seen or taken were fresh. 



During the next 10 days the numbers of all' the other autumn 

 butterflies — the butterflies that normally issue from the pupa at this 

 season — more or less gradually increased, so that in the last few 

 days of September these were scarcely less common than usual. Two 

 of them, indeed, the Camberwell beauty {Vanessa antiopa) and the 

 red admiral {Pyrameis atalanta)^ seemed to be rather unusually 

 numerous. This may have been due, however, to the fact that they 

 remained strictly in the damp woods, not straying widely over the 

 fields as is their normal habit at this season. On the other hand, 

 Colias philodice remained rather infrequent, and its numbers were 

 insignificant in comparison with those of C. eurytheTne. 



After the first of October the number of butterflies, in the absence 

 of any further showers, slowly decreased, and a brief survey of the 



