Aphids and Milkweeds

Share our info on aphids, other insects and native milkweeds.


Table for 200?

Image © Brian Henderson
By Andrés Ortega, Ecologist

The word is spreading: Monarchs need milkweeds. They’re the only plants their caterpillars will eat. It makes sense, then, that people concerned with the drop in monarchs in the U.S. are adding milkweeds to parks and backyard gardens. The plants’ stems and leaves provide an irreplaceable diet for caterpillars, and the flowers feed adult butterflies and bees. But as many gardeners will attest, those aren’t the only guests showing up for dinner.

Expecting to find only hungry caterpillars, many gardeners are alarmed when they see their milkweeds covered with tiny orange bugs: oleander aphids. Just like monarch caterpillars, these insects feed on the plants’ sap. They may be unsightly, but they’re typically harmless.

Still, many frenzied gardeners look for ways to rid their plants of aphids, from applying isopropyl alcohol, soaps, detergents and insecticides to bringing out the vacuum. But even the most benign methods — gently brushing the aphids off by hand or spraying them with clean water to wash them away — can harm monarch eggs and caterpillars, the reasons people planted the milkweeds in the first place

Fortunately, ladybird beetles, lacewings and other native insects love to eat aphids. Lacewing larvae in particular are known as “aphid lions.” To keep plenty on hand, gardeners often plant asters and sunflowers — favorite foods for adult lacewings — among their milkweeds.

Monarch caterpillars may eat nothing but milkweeds, but milkweeds provide important meals for a variety of insects. And as any bird, bat or frog with insects on its own menu will tell you, the more the merrier.
Image © Brian Henderson
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