What Are These Black Spotted Red Insects on the Milkweed Plants?

While keeping an eye out for Monarch butterfly caterpillars, I keep seeing the other types of insects that feed on Common Milkweed. I wrote an article recently introducing the Milkweed Tussock Moth caterpillar. This time, I’m talking about a type of beetle that is very common on Milkweed in southern Ontario, far more commonly seen that any of the caterpillars.

Photo of Red Milkweed Beetle Horns Out On NaturalCrooksDotCom

(There are actually several different red and black insects that feed on Milkweed plants in southern Ontario. One set are beetles and the other set are bugs. I’ll have to write a post on the bugs next.)

Milkweed Beetles Have Black Spots, Long Black Antenna, and Red Shells

Aside from the vivid black and red colouring, Red Milkweed Beetles are particularly noticeable because they have long black antenna. According to a University of Wisconsin website, they are a member of the long-horn beetle family, just like the Asian Long-horned Beetle that sometimes gets in the news when areas in North America are quarantined to eradicate it. These Red Milkweed Beetles, however, offer no threat to our forests and are native to North America.

Photo of Red Milkweed Beetle Flower Stems on NaturalCrooksDotCom

Do Red Milkweed Beetles Eat the Leaves of Common Milkweed?

Yes, adult beetles do eat the leaves. The young, however, eat the roots of the milkweed plants and live underground. This is quite different from Milkweed Bugs which are an unrelated insect.

According to BugGuide.net, they have been reported on other types of Milkweed but appear to prefer Common Milkweed.

Photo of Red Milkweed Beetle Top Leaf On NaturalCrooksDotCom

Does Eating Milkweed Make These Beetles Toxic to Predators?

When insects eat the sap in milkweed plants, they take in some chemicals called cardenolides (cardiac glycosides) that are poisonous to many mammals, birds and other animals. That does not mean that a Blue Jay who eats a single Monarch caterpillar will die: the jay will feel poorly though. Many insects that eat milkweed have bright colours, like these Red Milkweed Beetles, that may help cause birds and animals to avoid eating them again to avoid a second bout of illness.

Photo of Red Milkweed Beetle Sheridan Meadow B on NaturalCrooksDotCom

The toxicity of Milkweeds, including Common Milkweed, is one of the reasons that these plants used to be classified as a danger to livestock by many jurisdictions. It was often mandatory to spray and remove Milkweed because it can poison poultry, sheep, cattle and other grazers. Now due to extensive lobbying from Monarch-lovers many places have repealed these laws so that Common Milkweed can be allowed to grow along roadsides and in private gardens.

Do I Need to Kill Red Milkweed Beetles If I Want to Help Monarch Butterflies?

Photo of Red Milkweed Beetle Up On NaturalCrooksDotCom

No. Monarchs and Milkweed Beetles have co-existed for hundreds of years. There’s no need to destroy a normal healthy part of the food web just to help Monarchs.

Why I Look Forward to my Next Encounter with a Red Milkweed Beetle

According to one article I was reading, these beetles actually make sounds including a purr and a whine. I’ll have to try to tune in the next time I encounter some!

Photo of Red Milkweed Beetle Sheridan Meadow on NaturalCrooksDotCom

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Have you seen some of these long-horned beetles on your local patch of Milkweed? Did you hear any of them purr? Please share your sighting with a comment.

8 thoughts on “What Are These Black Spotted Red Insects on the Milkweed Plants?

  1. They eat leaves and flowers, no flowers no seeds I’ve started to pick them off in hopes of more seeds

  2. I just saw on2 of these beetles on my milk weed. No I didnt hear them purr…

    Just didn’t know what they are or if I should give them a burial or not. Lololo

  3. I’ve been letting the milkweed grow for the Monarchs but this is the first time I’ve seen red milkweed beetles — lots of them in my yard in Iowa. Don’t hear any sounds.

    • I’ve never heard of any danger from them but you can check with your doctor. Many insects will bite if they feel threatened. I see online that it’s more common to get bitten by a similar bug called a Milkweed Assassin bug. There’s a photo of one at http://bugguide.net/node/view/428983
      I’m sorry I can’t tell you if it’s ok or not but I’ve never heard or seen anyone who was bitten.

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