by Beth Weiler

Many of us love exploring Milkweed plants for the chance to find a chubby Monarch caterpillar: a sign that things are working and that the Milkweed is serving its big purpose. Monarch larvae are always an exciting find, but Milkweed plants are host to tons of other fascinating critters. This week’s bug spotlight shines on two such friends: the Milkweed leaf beetle and the Red milkweed beetle. If you’ve spent time examining Milkweed leaves, you may have encountered these two beetles, both of which display an interesting trait reflective of their Milkweed-eating existence.

The Milkweed leaf beetle, Labidomera clivicollis, is a very round and robust, brightly-colored beetle in the leaf beetle family (Chrysomelidae). It is most often bright red with black patches, but can be light to dark orange, too. My favorite thing about them is their feet, which, in non-technical terms, are adorable. The Red milkweed beetle, Tetraopes tetrophthalmus, is longer and more oval-shaped than L. clivicollis. It is in the longhorn beetle family (Cerambycidae) and has long antennae that actually bisect the beetle’s eyes, which makes it appear to have four eyes (hence, Tetraopes)!

So, why are both of these beetle species black and red? Don’t their bright colors and patterns make them obvious to predators? Actually, each beetle has evolved this particular coloration to warn potential predators to stay away and find something else to eat. Their Milkweed hosts contain a sticky white sap that is full of compounds toxic to anyone who ingests it…except the critters that have evolved to feed on it, like these beetles. As they feed on the Milkweed, the beetles absorb the toxic compounds and thus become toxic to potential predators, perfectly exemplifying the old adage “You are what you eat.” Their coloration is a big caution sign that reads, “I Taste Bad!” This evolutionary phenomenon of eating poisonous plants and displaying cautionary colors is called aposematism. It is the same reason that our beloved Monarch friends are black and orange, and their caterpillars black and yellow.

If you find these two striking beetle species on your Milkweed, enjoy observing them do their thing and definitely don’t try to figure out what they taste like.

Milkweed leaf beetle upside down on leaf

Milkweed leaf beetle.  Photo by Beth Weiler

Red milkweed beetle on leaf

Red milkweed beetle. Photo by Beth Weiler

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