monarchs and swan plants

Paul Cherubini paul at
Tue Jan 19 06:03:59 EST 1904

John Grehan wrote:

> It was my understanding that the monarch was already in NZ and Australia
> before human introduction of the host-plant, but that they were not able
> to permanently establish in the absence of the hostplant. I also understand
> that there is no migration phenomenon like that in America - is that correct?

A monarch biogeographer, Richard Vane-Wright has studied the situation in detail and 
found the monarch became established in Hawaii and many other central and south 
Pacific islands is the mid-late 1800's. This timing coincides with the advent of fast 
moving steam powered trading ships. It is interesting to note that the areas in Australia 
where the weedy swan plant became established are the same areas where the native 
eucalyptus forests were clear cut to accomodate agricultural interests.

The seasonal migration/overwintering phenomenon in Australia is just like that in America 
except the numbers of butterflies involved and the distances they travel are smaller. Right 
now is late autumn in the Sydney area and hundreds of monarchs can be found clustering 
in at least a dozen eucalyptus groves slightly west (inland) of the city. Clustering also 
occurs in New Zealand at this time of the year, but the migration there has no been 
studied in detail.

Paul Cherubini, Placerville, California

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