Yosemite and Tioga Pass Area

These yellow Oleander Aphids (Aphis nerii) with wiry black legs are often found on milkweed plants are yellow, soft, oval, and huddle together on new shoots, stems, buds, and leaves. They damage the plant by sucking liquid from the plant, eventually stressing the plant and killing it when infestation is high. Insecticides should never be used to kill the aphids, because this will also kill the Monarch Butterflies that visit the milkweed.