Large-Scale Migrations of the Painted Lady Butterfly, Vanessa cardui (Lepidoptera: Nymphalidae), in Inyo County, California, during 1991

Abstract

Detailed observations on significantly large migrations of Vanessa car- <br /><br />dui during 1991 in Inyo County, California, are presented, with special emphasis <br /><br />on their complex behavioral activities. The build up and mass exodus at a pop- <br /><br />ulation center near Bishop are chronicled and provide insights into why some <br /><br />butterflies migrate. A directional shift from northward to southward migration <br /><br />occurred during the summer. The migration phenomenon in this species appears <br /><br />to be dependent upon larval stress subsequently influencing adult juvenile hor- <br /><br />mone levels. This behavior likely evolved during the Upper Miocene as an ad- <br /><br />aptation to avoid seasonally unfavorable arid conditions.