Lepidoptera migration

Many populations of Lepidoptera (butterflies or moths) migrate, sometimes long distances, to and from areas which are only suitable for part of the year. Lepidopterans migrate on all continents except Antarctica, including from or within subtropical and tropical areas. By migrating, these species can avoid unfavorable circumstances, including weather, food shortage, or over-population. In some lepidopteran species, all individuals migrate; in others, only some migrate.

The best-known lepidopteran migration is that of the eastern population of the monarch butterfly which migrates from southern Canada to wintering sites in central Mexico. In late winter/early spring, the adult monarchs leave the Transvolcanic mountain range in Mexico for a more northern climate. Mating occurs and the females begin seeking out milkweed to lay their eggs, usually first in northern Mexico and southern Texas. The caterpillars hatch and develop into adults that move north, where more offspring can go as far as central Canada until next migratory cycle.

The Danaids in South India are prominent migrants, between the Eastern Ghats and Western Ghats. Three species will be involved in this, namely Tirumala septentrionis, Euploea core, and Euploea sylvester. Sometimes they are joined by lemon pansy (Junonia lemonias), common emigrant (Catopsilia pomona), tawny coster (Acraea terpsicore) and blue tiger (Tirumala limniace).

Migration in Lepidoptera means a regular, predictable movement of a population from one place to another, determined by the seasons. There is no unambiguous definition of migratory butterfly or migratory moth, and this also applies to proposals to divide them into classes. Migration means different things to behavioral scientists and ecologists. The former emphasize the act of moving whereas the latter discriminate between whether the movement has been ecologically significant or not. Migration may be viewed as "a behavioural process with ecological consequences".

...
Wikipedia