116 BULLETIN 15 7, U. S. NATIONAL MUSEUM 



In the District this butterfly apparently does not survive the 

 winter. It is exceedingly scarce early in spring, at which season I 

 have never seen it except near the river, in Potomac Park, in the 

 Smithsonian grounds, and in the meadows west of Cabin John, and 

 it is in this region, and also along the Eastern Branch, that fresh 

 butterflies first appear in June. 



I believe, therefore, that the District is repopulated each year from 

 regions nearer the sea by butterflies which wander inland, following 

 the banks of the river and of its larger tributaries. The adults from 

 the eggs laid by these immigrants scatter widely over the District, 

 and their successors become increasingly common and Avidespread 

 until the end of the season. 



Seasons. — The milkweed butterfly passes the winter in the adult 

 stage and appears on the wing late in April or early in May, just 

 before the milkweed {Asclepias syriaca) emerges from the ground. 

 The females lay their eggs on the little plants soon after they first 

 appear. Fresh butterflies are first seen early in June and increase 

 in numbers throughout the summer, the species being most common 

 in the middle or last half of September and continuing on the wing 

 until the latter part of October. The autumn butterflies, which con- 

 tinue to emerge up to the very last warm days of the season, prob- 

 ably for the most part represent a third brood, some representing a 

 second brood, and a very few a fourth brood. In the first frosts 

 all the eggs, caterpillars, and chrysalids are killed, and the hiber- 

 nating adults die during the winter. 



Habits. — The flight of this butterfly is rather slow. Over flower- 

 filled meadows it flies usually from 6 inches to a foot above the tops 

 of the goldenrod and asters, progTessing at the very leisurely rate 

 of about 7 miles an hour. But over barren pastures it keeps 3 or 4 

 feet above the short grass and travels at the rate of about 15 miles 

 an hour. It flies with a few rather slow flaps alternating with long 

 glides during which the wings make with each other an obtuse angle 

 of about 120° and the insect teeters or sways from side to side with a 

 curious seesawing motion. From time to time the butterfly, in broad 

 curves to one side or the other, slightly changes its course, but the 

 same general direction usually is maintained. It is not given to 

 quartering irregularly about within a more or less limited area, as 

 are nearly all our other butterflies, but spends most of its life cruising 

 along in an aimless sort of way. Late in summer the -contrast 

 between the manner of flight of this butterfly and that of the com- 

 mon clover butterflies {C alias eury theme and C. philodice) frequent- 

 ing the same fields is very striking. 



The milkweed butterfly is particularly fond of flying along the 

 seacoast or along the bank of a broad river, and it will do this even 

 in the presence of a strong onshore or other wind. It is commonly 



