INSECTS 203 



(1925). The only known instance of the return migration of the same 

 individuals is afforded by the monarch butterfly {Anosia plexippus L.), 

 though it is not improbable that Pyrameis atalanta L. may exhibit a 

 similar behavior. The monarch probably owes this unique ability to 

 its remarkably strong flight, as well as to the fact that it is one of 

 the longest-lived species of its order, hibernating in winter in the 

 South as enormous masses in the treetops. Some butterflies, such as 

 Pyrameis cardui L., display a special type of migration in which the 

 adults fly north to lay eggs and the young travel to the south in the 

 fall. IMass flights of dragonflies occur at infrequent intervals and 

 are probably to be ascribed to migration in search of breeding places, 

 especially when drought has dried ponds and marshes. Local diurnal 

 migrations are common (Beklemischev, 1934; Carpenter, 1935). 



Grasshopper migrations which have resulted in their invasion of 

 cultivated areas with devastating effects are known to have occurred 

 since the beginning of historical records (Exodus 10: v. 13-15; Figuier, 

 1868) in all temperate and tropical areas of the world (Thomas, 1880; 

 Uvarov, 1928). The early accounts are much exaggerated except for 

 local areas, as the grasshoppers rarely devour all the herbage or foli- 

 age, and the presence or absence of food is usually not the cause of the 

 departure of the insects, either in their initial movements or after a 

 stop. 



The chief migratory locust of North America is Melanoplus mexi- 

 canus Sauss., the solitary phase of which was formerly M. atlanis 

 Riley, and the migratory, M. spretus Walsh. This species has been in 

 outbreak and has migrated from the Rocky IMountain area into the 

 states immediately west of the Mississippi at various times, notably 

 1874-79. Parker (1930), working over a period of years in Montana 

 and ]\linnesota on temperature relations of this species, found that the 

 activity is controlled by temperature, the average low temperature for 

 the beginning of movement of nymphs being 16.3° C. and of adults 

 16.6° C. Normal activity of nymphs takes place from about 18° C. 

 to about 33° C, and they migrate in bands or clusters from about 

 22° C. to 34° C. Feeding begins with normal activity, but ceases at 

 about 27° C, the insects climbing into vegetation to escape the heat. 

 Under falling temperature, at 20° C. to 21° C, the grasshoppers start 

 clustering in warm sunny places and arrange their bodies so as to 

 secure the maximum heat from the sun's rays. 



Referring to the adults, Thomas (1880:155) states that flight be- 

 gins on warm days, but that there is none on days with a maximum 

 of 21° C. and a minimum of 16° C. Swarms arrive on a warm day, 

 alight in the late afternoon, and remain for several days. He further 



