120 BULLETIN 15 7, U. S. NATIONAL MUSEUM 



viciously a hummingbird so incautious as to approach too near the 

 flower on which it is feeding, always badly frightening the bird, which 

 makes off in a straight line as fast as possible. After one of these 

 attacks on a hummingbird the butterfly always displays intense ex- 

 citement for some minutes. Prof. Walter K. Fisher tells me that 

 Mrs. Fisher has seen this butterfly in the same way attack and put to 

 flight a warbler at Pacific Grove, Calif. The Camberwell beauty 

 (Vanessa antiopa) is the only other of our local butterflies that I 

 have seen attack birds, and in this case small warblers (Mnio- 

 tiltidae) are the victims. The attacks on birds by this last-named 

 insect seem to be in the nature of routine performances and are not 

 followed by any evident excitement. 



The fundamentally peaceful nature of the large, conspicuous, and 

 rather slow and clumsy milkweed butterfly seems to be well known 

 to the other kinds of butterflies, and late in summer it is frequently 

 persecuted by the pugnacious males of other species, particularly the 

 pearl crescent {Phyciodes tharos), the buckeye {Junonia lavinia), 

 the viceroy {Bas^ilarchia archipfus)^ and the hop merchant {Poly- 

 gonia comma). It is almost invariably attacked if it happens to 

 cross a road where these are disporting themselves, and the little pearl 

 crescent is always ready to attack it — anywhere and at any time. 

 When attacked it increases its speed, rises slowly upward, and dodges 

 awkwardly about in an effort to shake off its pursuer. The obvious 

 fear of the little pearl crescent — which could not possibly do it any 

 damage — displayed by the milkweed butterfly is as ludicrous as it is 

 difficult to understand. 



In the milkweed butterfly all the surplus energy of both sexes 

 seems to be expended in traveling, and these insects, especially the 

 females, spend a far larger portion of their time upon the wing than 

 do most butterflies. 



The milkweed butterfly is remarkable in that there seems to be a 

 minimum of difference in the actions and habits of the two sexes, and 

 throughout the territory inhabited by it they occur in the same pro- 

 portion — in practically equal numbers. In flight the males are readily 

 distinguishable by their brighter color. 



Mating takes place in open grassy fields, especially along the borders 

 of woods. The eggs are laid for the most part on isolated milkweed 

 plants or on the more detached peripheral plants of small scattered 

 groups growing in open fields and especially along the borders of 

 woods and along roadsides. Very often plants are chosen which are 

 growing close to a building, wall, or fence. The eggs are seldom, per- 

 haps under ordinary circumstances never, laid on plants growing in 

 large dense stands. 



When engaged in laying her eggs the female flutters about the 

 plant in a somewhat clumsy way, from time to time hitting the 



