180 BULLETIN 15 7, U. S. NATIONAL MUSEUM 



on the buttonbush, and toward the season's end on thistles, on iron- 

 weed, and on joe-pye-weed and related species. 



When feeding the wings of the females and of the larger males are 

 held motionless and fully extended, with the fore wings drawn well 

 back, the attitude being quite the same as that assumed when enjoy- 

 ing the warmth of the sun's rays. Because of this peculiarity, as 

 well as by its less hurried and less irregular flight, the black form of 

 the yellow swallowtail is in life readily distinguishable from our 

 three black swallowtails. The small males flutter their wings more 

 or less continuously when feeding, somewhat after the fashion of the 

 parsnip swallowtail {P. polyxenes). 



Of all our swallowtails this is the most fond of carrion and of 

 fllth, which seem to have an irresistible attraction for it and about 

 which it will sometimes gather in surprising numbers. Not infre- 

 quently it will so gorge itself with liquid from a rotting carcass as to 

 become helplessly intoxicated. 



It is also very fond of congregating on muddy spots in roads, on 

 the damp earth on the side of pools or ponds, or puddles in the half 

 dry beds of streams. It frequently is seen, often several or even many 

 at a time, hovering about wet spots near barns or houses. 



The males are more active and more restless than the females, more 

 constantly on the wing, and more given to playing about the trees 

 and to wandering. 



The small individuals common in spring are more active and shier 

 than the large individuals of the summer broods, and also they seem 

 less inclined to wander. At any rate early in spring this butterfly is 

 much less often seen away from woods than later in the year, though 

 this may in part be due to the lesser number of the individuals. 



Broods. — There are two broods a year. The butterfly first ap- 

 pears in the first week in April, and individuals continue to emerge 

 until about the middle of June. During June the numbers decrease, 

 and by the last week in the month the species has almost completely 

 disappeared. The males have been flying for a week or more and 

 have become common at the time of the first appearance of the 

 females. The earliest individuals of both sexes are ahvays of small 

 size. As spring advances the size of the individuals gradually in- 

 creases, so that the late individuals of spring brood are as large as 

 the majority of the individuals of the summer brood. Occasional 

 males of the second brood appear about the middle of June, and by 

 about the first of July or shortly after the butterfly has become 

 common. Individuals continue to emerge nearly throughout August, 

 but after the middle of August the numbers fall off, and in Septem- 

 ber only worn individuals are found, a few of which may still be 

 seen as late as the middle of October. The individuals of the second 

 brood are much more numerous than are those of the first. Practi- 



