I found these aphids covering my first planted milkweeds. After discovering what they were, an aphid not native to our area, I squished them. Yuck! But that year, I could not keep up with them and they ended up eating the plants to the ground. The Monarchs didn't find them that year, nor any of the other milkweed specific insects.
This year Swamp Milkweed came up in a new place and I planted dozens of Butterflyweeds. The Monarchs found them early on and most of the caterpillars were done before the aphids arrived. The aphids were much more manageable this year, so I was able to keep up. I was eager to collect seeds this year, so doubly wanted to make sure the plants would make it.
