One of the more common comments we hear in the Flight Encounter here at BioWorks is, “Wow, there are a lot of eggs on your milkweed!” Usually, what the visitor has noticed are not actually eggs at all – they’re aphids (Aphis nerii), which love to infest milkweed plants to enjoy the sticky sap. They can eventually cause damage to plants, so butterfly gardeners may wish to identify and control these little pests so Monarchs and Queens can use these plants instead.
It’s also possible to confuse monarch eggs with those of the lacewing, Lacewings lay their eggs in a pretty unusual way, though, placing each at the end of a delicate string (click here to see a picture). Monarch eggs will always be directly attached to the leaf, stem, or flower.
Getting rid of aphids can be a bit tricky. If there are only a few, you can pick them off with your fingers (wear gloves or expect your fingers to take on a lovely saffron hue). The best way is to spray them with the hose at close range – the water pressure will wash off most of the aphids but generally won’t dislodge the monarch eggs. Don’t apply pesticides, including insecticidal oil, as that will kill caterpillars and eggs too.
What about ladybugs? Ladybugs are natural predators of aphids, and many people release them in their gardens as “friendly insects”. Unfortunately, ladybugs will also prey on caterpillar eggs, so they’re not a great solution in the butterfly garden. (Don’t try to completely eliminate ladybugs from your garden, though – they’re an important part of the natural balance.)
This is very educational. Thanks for posting it. It's true that the most easiest way to distinguish a caterpillar egg from a an aphid is through color. However, in eliminating aphids with the use of a hose, is it possible that you could also cause damage to caterpillar eggs?
ReplyDeleteDavid Wofford
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David - Caterpillar eggs are attached fairly firmly to the plant, and usually aren't dislodged by the use of a hose. While one or two may get knocked off by the water, most should be fine. Thanks for reading!
ReplyDeleteMy milkweed is totally infested with aphids--too many to pick off, I didn't realize what they were3 until too late....Can I use plain old dish soap and water on them---will it hurt the cats?
ReplyDeletePut a little dish soap and some water into a spray bottle and spritz down the aphids. The soap will taste terrible to the cats so they will likely avoid it. Your cats will probably also avoid the milkweed entirely because the sap is incredibly bitter and a bit toxic if ingested.
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