Aphis Nerii, Oleander Aphid

While I normally take great joy in announcing a new find, I am not exactly thrilled with having discovered an infestation of Oleander Aphids (Aphis nerii) on one of my milkweed plants. The field guide says, "Its bright colors advertise the fact that this species is chemically defended, thanks to chemicals borrowed from their host plants." What, you couldn't have guessed from the black spines (cornicles) sticking up from their backs? The bright orange colour and black legs/cornicles differentiate this species from another less orange aphid, A. gossypii. Although the ants were doing their damndest to get the infestation under control, I took soap spray to the infected pods and leaves. This particular aphid is an introduced species.