I think the allegedly discrepancy between their weight and their ability
to fly has something to do with the fact that their wings rotate, so
that calcualtions for a fixed wing are not correct.  I have noticed,
but not read, several articles in science and physics journals on the
topic of bumblebee fligth in the last year or so. Perhaps a keyword
search would pull them out.
 
Liz Day
 
University of Illinois at Chicago
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