I wondered why I kept seeing so many monarchs come to my milkweed but still had no eggs or caterpillars. Then I did a little research and discovered I was seeing male butterflies. The males have 2 black oval spots on the bottom wing quarters on either side of the end of the abdomen, as you can clearly see in this photo.
Monarch Butterfly (Danaus plexippus)
SUNSET / BLOOD FLOWER Scarlet Milkweed (Asclepias Curassavica)