The Monarch is probably the most popular butterfly there is.  It sometimes lays its eggs on my Butterfly Weed and Swamp Milkweed plants.  I used to see Monarchs beginning early in the summer every year.  Recently, they haven't been coming around until September.  I have seen as many as 20 in my garden at one time.  The most I've seen at one time in the past three years was two.