Anyone growing milkweed has had these little vampires invading their plants. Non native, they usually show up late summer early fall and can heavily infest plants in a short time
Each spring, when the temperatures and other weather conditions are just right, winged females are blown long distances on the wind. When the air becomes calm, the aphids can make directed flights to host plants. Experts have failed to find male oleander aphids in North America,
so they believe the winged females produce young without mating (called parthenogenesis). The first offspring are female aphids without wings. The aphids continue to give live birth to more aphids until conditions cause winged forms to be produced. The winged forms move on again.
Unlike many other introduced insects, oleander aphids have a number of parasites and predators. You may have seen the results of tiny wasps (for example, Lysiphlebus testaceipes). The female wasp lays its egg by inserting its ovipositor within the young aphids. The wasp's larva then eats the aphid's insides. When the parasite goes through metamorphosis into a pupa inside the body of the aphid, it causes the body of the aphid to turn brown, tan or black, and stiffen. This immobile aphid is referred to as a “mummy.” When the wasp emerges from the pupa, it cuts a hole in the back of the aphid’s abdomen and flies away, leaving the aphid’s empty body.
Manually removing is always the preferred method of keeping the aphid population in check but can be rather messy if you don't where gloves. Early detection can make the job easier . Other methods include hosing with water , dish soap solution, and alcohol. Aphids will not harm monarch caterpillars/eggs nor will they kill the plant