Butterflies do lay their eggs on the foliage of some perennial plants and also native weeds such as milk weed, the preferred food of the Monarch butterfly. There is no need for you to worry about destroying the eggs of Monarchs this fall however. The butterflies will be heading south for the winter and then returning in the spring to start laying eggs for next summer. The best thing you can do for bees and  butterflies is to have a variety of plant material in your garden with plenty of flowers that bloom at different times of the year. The Buddleah or butterfly bush, salvias and sage, sedum 'Autumn Joy' and early blooming plants such as pulmonarias and plants native to your area all help bring butterflies to the garden. Keep growing, Marianne Binetti