Autumn Migrations of Butterflies 



Bv HOW A KM) .1. SHANNON 



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SYSTEMATIC studies of the sea- 

 sonal migrations of insects have 

 always been attended by difficul- 

 ties which are sufficiently obvious. The 

 elusivencss, when in full flight, of the 

 subjects themselves, the difficulty of 

 distinguishing a merely local movement 

 from an extensive advance, as well as 

 the wide geographical range of various 

 species wdiich may be considered mi- 

 gratory, so that it is impossible to dis- 

 tinguish incoming travelers from the 

 resident population — all these are 

 drawbacks which have stood in the way 

 of more definite information. There- 

 fore it is not surprising that we have 

 such fragmentary knowledge of the 

 species which do migrate, as well as of 



the laws which govern them in their 

 annual behavior. 



In fact, there is a large and impres- 

 sive body of opinion which questions 

 whether butterflies take part in sea- 

 sonal movements with any real con- 

 stancy and regularity in temperate 

 North America, except in the case of 

 the "monarch" (Atiosia plexippus), 

 and the ''great sulphur" (Cotopsilia 

 euhiile), which certainly move south in 

 autumn and north in spring. In addi- 

 tion to these, of course, there are the 

 dispersal movements from the south in- 

 volving certain butterflies and, more 

 particularly, moths like the cotton moth 

 (Aletia arf/illncea) and the velvet bean 

 moth ( Anticarsia gemmatilis) , which 



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MONARCHS IN MIGRATION. 

 <^«-*< MIGRATIONS OF G R A P TA . P YR AMEIIS, JUNONI A 

 AND OTHER BUTTERFLIES. 



Autumn migrations of butterflies on Long Island. Fluctuation in numbers of migrating butterflies 

 from day to day is apparently due to changes in wind direction, so largely also a controlling factor in the 

 migration of birds. Migration is much more profuse along the Long Island coast on days when the wind 

 is north or northwest 



1 Article and illustrations copyrighted, 1917, by Howard J. Shannon. 



33 



