Each year at this time things get a little bit spooky at Bug of the Week and we celebrate a few styling bugs dressed in Halloween colors. Perhaps the most famous insect in orange and black is the spectacular and beleaguered monarch butterfly we met a few weeks ago when we learned of its perils in North America and abroad. We also met another denizen of the milkweed, the hairy milkweed tussock moth caterpillar. This week we visit another stunning insect member of the orange and black gang, the delightful milkweed leaf beetle.
This beetle is a relative of the dogbane leaf beetle and Colorado potato beetle we met in previous episodes. Adults and larvae of this gorgeous insect eat leaves of milkweeds growing wild in meadows and also the butterfly weed running rampant in my perennial beds. Like summer itself, milkweed leaf beetles arrived late this year. A few adults that survived the polar vortex appeared several weeks ago and somehow discovered the small patch of butterfly weed in my front flower bed.
Beautiful adult milkweed leaf beetles sport the warning colors of orange and black.
Adult beetles are voracious feeders and they quickly removed large slices of the leaves. Leaf protein is translated into batches of eggs within the female beetle. About a week after eggs are laid, rotund orange beetle larvae hatched from these eggs and grazed mightily on my milkweed. Larvae move to the soil to pupate and by September a fresh batch of adult beetles had emerged and colonized the milkweed. Adults of this generation fatten up on milkweed leaves before finding a protected refuge somewhere in my garden to spend the winter.
Why is milkweed the perfect plant for attracting and maintaining so many bugs in orange and black? From the leaves and milky sap of milkweed, insects like the larvae of the monarch butterfly obtain potent defensive chemicals known as cardiac glycosides. These compounds are stored in the bodies of caterpillars and adults alike. Visually gifted predators like birds regularly prey on insects of many kinds including caterpillars, butterflies, and beetles. Cardiac glycosides found in the wings of monarchs are known to cause severe digestive distress to avian predators. The conspicuous orange and black colors of the monarch serve as a reminder of a nasty gastronomic misadventure to experienced birds that once attempted to eat a monarch. Unlike the monarch, larvae and adults of the milkweed leaf beetle are not thought to sequester cardiac glycosides from their milkweed host. However, they have adopted the orange and black coloration of the monarch and other denizens of milkweed. The orange and black color scheme may be sufficient to deter enlightened predators from risking an attack on a potentially nasty meal.
Amidst a serenade from birds, crickets, and cicadas, a portly milkweed beetle larva searches for tender leaves of milkweed on which to feast.
The delightful book “Secret Weapons” by Thomas and Maria Eisner and Melody Siegler was used as a reference for this episode.
To learn more about insects found on milkweed, please visit the following web sites: