Monarch Egg or Aphid? How to Tell the Difference

Not sure what you've got on your milkweed plants? Learn to tell the difference between a monarch egg and an aphid.

So, you’ve read the sober news reports about the decline of monarch butterflies, and decided to do something about it. You filled your garden with native milkweed plants, which are growing big and strong. You’ve even seen the brilliant orange wings of monarchs fluttering around your garden. Now it’s time to check the plants to see if you’ve had any success. You see something tiny on the leaves—but is it a monarch egg or something else?

Monarch Egg or Aphid
This plant has both aphids and a monarch egg. Can you spot both?

Here’s how to tell whether you’re looking at monarch eggs or aphids in three easy steps.

What Do Monarch Eggs and Aphids Look Like?

  • Aphids are bright yellow.
  • A monarch egg is white or off-white. It’s ovoid in shape, and if you look very closely with a magnifying glass, you’ll see vertical ridges along the sides. As the tiny larva inside develops, the egg will darken slightly in color before hatching in about 3 – 5 days.

Do You See Legs or Movement?

  • Aphids are insects with six legs. If you see wriggling black legs, you’ve got aphids.
  • Monarch eggs, of course, do not have legs. They also do not move.

One or Many?

  • Aphids tend to cluster in large groups along the stems.
  • You’ll usually find a single monarch egg on its own, often laid on the undersides of leaves. However, you may also find them on stems and flowers.

Monarch Egg or Aphid

Monarch Egg or Aphid
Single monarch egg on the underside of a leaf

How to Get Rid of Aphids

So, you’ve got aphids on your milkweed. The good news is that they’re unlikely to deter monarchs from laying eggs or keep the caterpillars from developing. However, a bad enough infestation can weaken the plant, and they look pretty unattractive. So how do you get rid of them?

First, and most important: NO PESTICIDES. THIS INCLUDES INSECTICIDAL OIL AND DISH SOAP. These will kill any monarch eggs or caterpillars already on your plant. Instead, my preferred way to remove aphids is with a strong blast from a garden hose. Rinse the aphids from the plants using your fingers under the running water. You may not get them all, but it will be enough to make a difference. This solution doesn’t last long, so you’ll need to do this once a week or so. Or, just learn to live with the aphids if you can. The monarchs won’t mind if you don’t! Check out more natural ways to eliminate garden insect pests.

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Jill Staake
Jill lives in Tampa, Florida, and writes about gardening, butterflies, outdoor projects and birding. When she's not gardening, you'll find her reading, traveling and happily digging her toes into the sand on the beach.