the mystery of Vanessa unidirectional migration

Patrick Foley patfoley at csus.edu
Mon Apr 30 22:45:26 EDT 2001


Liz and other flagrant favorers of the furry fliers,

Vanessa cardui does appear to migrate South in the Fall. How extensive this is
I do not know, but see
1) Emmel T. and R. A. Wobus 1966.  A southward migration of Vanessa cardui in
late summer and fall. J. Lep. Soc 20:123-124. In Colorado USA
2) R. Robin Baker 1978. The Evolutionary Ecology of Animal Migration. Holmes
and Meier, New York. p 431-432 where he discusses and maps the return
trajectories of "Cynthia" cardui.

It is worth remembering that almost all organisms, especially butterflies and
humans, are descended from ancestors who, perhaps too crowded to be fit at
home, took to the road to find underutilized resources. It was a stupid shot in
the dark, but it works for the lucky survivors.

Patrick Foley
patfoley at csus.edu

Liz Day wrote:

> I don't understand what advantage this bug gains by migating north every
> spring, if the adults don't then migrate back south in the fall, and (?)
> thus their offspring are instead killed off by winter.  Isn't this genetic
> suicide?   I understand dispersion is good, but it seems like consistent
> directional dispersion in a direction that is ultimately death would be
> selected against, eventually.   What is going on?  I must not be seeing the
> whole picture.
>
> Thanks,
>
> -------------------------------------------------------------
> Liz Day
> Indianapolis, Indiana, central USA  (40 N, ~86 W)
> USDA zone 5b.  Winters ~20F, summers ~85F.  Formerly temperate deciduous
> forest.
> daylight at kiva.net
> www.kiva.net/~daylight
> -------------------------------------------------------------
> "It is quite remarkable, when you think of it, that if you tell somebody to
> buy something and dump it on or squirt it on, he will almost certainly do
> it, after a fashion. But if you suggest that he observe something or think
> about something or learn about something, he almost certainly will
> not. Yet those gardens we admire are never the results of dumping and
> squirting: they are always the result of muddling things about in the brain
> and the eye."
> -- from _The Essential Earthman_, by the late Henry Mitchell
>
>
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