Query: "birds and bees"

[Cohen, Gerald Leonard]

Today in my Etymology class a student asked me about the rationale for the expression "the birds and the bees."  I mentioned that it's a euphemism for "sex/reproduction," but is there anything else to add?  When did the expression first appear, and why specifically where the birds and bees selected?  Why not, for example, rabbits and lizards? Or chipmunks?

Gerald Cohen

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