'Common milkweed' is a common name for 'Asclepias syriaca'. Other common names include 'Butterfly flower', 'Silkweed', 'Silky Swallow-wort', and 'Virginia Silkweed'. A favorite among the names is 'Butterfly flower'. That's because the wildflower's leaves are food sources for the caterpillar stage of the Monarch butterfly [Danaus plexippus]. Its nectar is a food source for the butterfly.
The milky liquid that's within the plant, and which the caterpillars access, results in foul-tasting Monarch butterfly caterpillars and Monarch butterflies. In fact, nature's predators are warned, because of the butterfly's bright colors. Specifically, in nature, oranges and fire-engine reds often advise potential predators of disgusting or toxic tastes.