Sounds like (1) you need to divide your milkweeds come this fall and (2) aphids are the black bugs.
(1) Late this sumer or early fall, divide your MW's by taking a good shovel and splitting the crown in half, digging up one half, and moving it somewhere else. You must do this, though, with a month or so before freezing so the roots can "take".
(2) the aphids are harmless, but you can squish them with a gloved hand, hose them with a good jet of water, "soap" them, or just leave them. I leave them and nothing negative happens because I am always harvesting leaves for the caterpillars that I raise and new ones grow in.
You can read many online articles on both topics above.