48 BULLETIN UNIVERSITY OF MONTANA. 



The fact of Northwaru movement in the spring is not so easily estab- 

 lished. As before stated the Anosia is not reported to have been found 

 North of latitude 31 degrees in the winter. When Spring opens n3ither 

 the egg, pupa or adult is to be found. The milkweed is a foot high in 

 Iowa and much good fodder is awaiting the larvae, before the adult makes 

 its appearance, and lays eggs on the tender unfolding leaves near the tip 

 of the growing plant. Some say that the appearance is not that of a 

 tattered "left over," as is usually the case with hibernating species. They 

 appear as a whole to be a fresher and newer lot; though I have seen 

 some that looked a good deal the worse for wear rather early in the sea- 

 son. There seems little doubt, however, that the new arrivals have not 

 hatched in our region, since there has been no opportunity for larvae 

 to develop and pupate. It seems more probable that they are the spring 

 brood from an earlier season in the south. We must not, however, con- 

 luse them wKh those that disappeared in that airection last fall. 



In Southern Iowa it seems probable that the eggs laid by the first 

 arrivals produce a new brood in July. These in turn produce the brood 

 that soon after arriving at maturity southward. We seem to have 

 two broods; while New England and northern climes have one only, and 

 that one, from the eggs of the first brood hatched in our latitude. The 

 northward migration is continued to Hudson Bay and north of the range 

 of the food plant of the larvae; a significant fact, in itself, proving the 

 migration of the species. The northern boundary of the food plant limits 

 the adult of other species sharply. This is noticeably the case with 

 Papilio ajax in southern Iowa, where a species very abundant south of 

 us is limited by the food plant, the Pawpaw, which disappears near the 

 40th parallel. 



There are several known peculiarities of this insect that especially 

 fit it for this sort of a life. The well known immunity from molestation 

 by insectivorous birds, the comparatively long intervals between oviposi- 

 tion, enable a butterfly of this species to scatter its progeny over a great 

 territory, since but one egg is laid in a place. The slow northward 

 movement of the season in spring allows time for additional broods fur- 

 ther South. The adults that first arrive here in the spring are sup- 

 posed to be from larvae grown several hundred miles to the southward, 

 w^here there may be four or more broods in one season. This north- 

 ward movement may therefore be considered a sort of a relay race. The 

 returning hosts contain none of the brood that came northward, since the 

 life of an insect after final oviposition is usually short and its excuse for 

 existence has expired. 



Granting that the seasonal migration of this butterfly is established, 

 we may say that this is merely another way in which nature replenishes 

 the earth after the life destroying frosts of winter, so fatal to insect life. 

 Hibernation has its advantages, and does not call for so complex an adap- 

 tation. Why Anosia has this different means of preservation is as much 

 a puzzle as ever. This illustrates anew a striking observation by Mr. 

 Frank Springer, the paleontologist, when sepaking of the marvelous 

 perfection to which an organism may be brought through a period of 

 development, only to be apparently discarded and the whole problem 

 worked out in an entirely different way in succeeding forms. He says 



