272 



THE GUIDE TO NATURE 



m*&M$ 



Migrations of the Cotton Moth. 



BY S. F. AAROX, 246 S. 5ISt STREET, 

 PHILADELPHIA, PA. 



The city of Philadelphia this past 

 season, during the latter part of Sep- 

 tember, received a visit from the well- 

 known cotton moth, Aletia argillacea. 

 The books record such instances, the 

 visits of the moth in great numbers as 

 far north as Canada and there has been 

 some discussion as to the actual ex- 

 tent of the migrations. Though strong 

 of wing, as are all of the family Noc- 

 tuidae to which this species belongs, 

 it is altogether evident that unless the 

 insects in great numbers flew very 

 high and were then favored by a hard 

 and direct wind from south to north 

 they would not be able to traverse a 

 distance of at least a thousand miles, 

 from the cotton belt to the 40th parallel 

 and above it. 



It is true that migrations of insects 

 do occur for considerable distances. 

 Darwin records flights of a species of 

 butterfly for several miles over the 

 ocean, Pyrameis cardui is known to fly 

 in direct migrations for nearly a hun- 

 dred miles, while the migrations of the 

 milkweed butterfly Anosia plexippus 

 are well known. The writer has ob- 

 served a species of the Pieridae, 

 Kricagonia lyside, migrating over the 

 Southwestern prairie in enormous 

 numbers and it was accurately deter- 

 minded that they traveled for over a 

 hundred miles. Certain mosquitoes 

 also, notably the Salt Marsh Culex so- 

 licitans, for no apparent reason and ap- 

 parently against its interests in the 

 matter of propagation flies high during 

 strong sea breezes, a habit altogether 

 at variance to that of most species, and 



it is wafted far inland where it can find 

 no place to breed and from which it is 

 quite unable to return. It would seem, 

 therefore, that Nature does not always 

 order things for the best in this regard 

 and that without apparent gain certain 

 species journey hither and yon for no 

 apparent purpose. On the other hand 

 we are acquainted with the long flights 

 of grass-hoppers to greener fields and 

 fresher vegetation and of many species 

 of dragon-flies from arid to watered 

 regions. 



It is evident that the cotton moth 

 caterpillar feeds commonly and often 

 in great numbers upon wild plants 

 probably related to the cotton plant 

 and inhabiting the temperate zone. 

 That this has not been positively re- 

 corded is not altogether strange ; there 

 is much unknown regarding the nat- 

 ural history of all but the larger and 

 more economically important moths. 

 That the species is occasionally very 

 abundant in certain areas, like many 

 other species, as the army worm, the 

 milkweed butterfly, the tussock moth 

 and caterpillar is due to the previous 

 reduction in numbers of its parasitic 

 enemies, from causes that have not 

 been discovered. Probably epidemics 

 of fungus diseases that commonly at- 

 tack both the Diptera and Hymenop- 

 tera the orders to which the parasites 

 belong, are at first responsible for the 

 entire circumstances. 



The cotton moths in this latter mi- 

 gration were all freshly hatched and 

 perfect specimens when they first en- 

 tered the city and its environs. They 

 flew through the streets of the business 

 center, swarmed about the electric 

 lights and lighted windows, fell in 



