The nectar of the flowers attracts many kinds of insects, including long-tongued bees, short-tongued bees, wasps, flies, butterflies, skippers, and beetles. Among these, bees and wasps are the more effective pollinators. Predatory insects often lurk near the flowers, including Phymata fasciatus (Ambush Bug) and Mantis spp. (Mantids). The caterpillars of the butterfly Danaus plexippes (Monarch) feed on the foliage and flowers. The species Aphis nerii (Yellow Milkweed Aphid) sucks juices from the upper stems and leaves. These aphids often attract ants (which feed on their honeydew), as well as Ladybird Beetles and Green Lacewings (which feed on the aphids themselves). Other insect species that feed on this and other milkweeds can be found in the Insect Table. Mammalian herbivores usually avoid this plant as a food source because of the bitter white latex, which is also poisonous. Whorled Milkweed is among the most poisonous of milkweeds, containing a high concentration of cardiac glycosides. Cattle have been known to poison themselves on this plant, but they rarely eat enough of it to produce fatal results.