. The American entomologist. Entomology. THE AMERICAN ENTOMQLOGIST. gregate and migrate in vast bevies, and numerous instances in several different Orders of insects might be cited. It has been especially noticeable in butterflies and moths, however, and European papers have lately very freely recorded the extra- ordinary abundance of Vanessa cardui and Pliisia gamma, the flights and movements of which were a marked feature of the year 1879, and phenomenal. Such occasional migratory movements are beyond doubt a result of multiplication, due to unusually favorable conditions for the
. The American entomologist. Entomology. THE AMERICAN ENTOMQLOGIST. gregate and migrate in vast bevies, and numerous instances in several different Orders of insects might be cited. It has been especially noticeable in butterflies and moths, however, and European papers have lately very freely recorded the extra- ordinary abundance of Vanessa cardui and Pliisia gamma, the flights and movements of which were a marked feature of the year 1879, and phenomenal. Such occasional migratory movements are beyond doubt a result of multiplication, due to unusually favorable conditions for the de- velopment of the species, but the conviction has been of late years forcing itself upon our minds that, with some butterflies, there are regular annual migrations that are more to be likened to those of birds of passage [Fig, toward the south and southeast in the Fall of the year, and in the very opjiosite direc- tion the ensuing spring. In the vast plains and prairies lying to the north between the Mississippi and the Rocky Mountains, upon the richer parts of which milk-weeds abound and Danais archippus more particularly flourishes and multiplies, there is a very general want of such protecting forest as will permit of hibernation, even if the but- terflies could withstand the severe winter of the sub-boreal zone, in which they may be seen in such large numbers during the summer. The more densely timbered re- gions to the south and southeast, as well as the milder winters, undoubtedly offer more favorable hibernating conditions, and we believe that there is an instinctive move-. Danais archifpu than to the more erratic and irregular in- sect-flights alluded to. The same laws which govern the move- ments of the Rocky Mountain Locust and cause it to move southward and southeast- ward during the latter portion of the grow- ing season, and its issue to return in the opposite direction in spring and early summer, seem also to govern some of our more widely distributed butterfli
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