A while back I wrote an article about using Diatomaceous Earth for natural, non-toxic flea control.
http://www.roadsend-papillons-phalenes.com/2011/06/diatomaceous-earth-for-papillons-dogs_19.html
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I would like to add another alternative, as far as keeping the fleas off of our beloved Butterflies the natural way.
Nematodes
These microscopic worms eat flea larvae, and will keep the flea population down in your yard.
You may purchase nematodes in your local pet, or garden/feed, seed store, or on line as for example Amazon does.
You place them in moist, shady areas in your yard, as these worms, nor the fleas do survive in the sun.
A lawn sprayer can also be used to apply the worms , and after about 24 hours you have reduced the flea population up to 80%.
See also
Flea Allergy
Tear Stains