June 2, 2021

It’s well known that milkweed attracts many different species of insects. The milky, toxic, latex-like fluid running through its veins renders the various insects toxic themselves. Many of the insects that consume milkweed leaves, buds, flowers or seeds are brightly colored as to warn predators not to eat them. They’ll get a foul taste in their mouths if they do. The red milkweed beetle is one of those toxic insects.

Red milkweed beetles are typically one of the first of the season milkweed specialists to arrive here in the museum’s Butterfly House Garden, catching the milkweed in its early stages.

The beetles consume the leaves, buds and flowers, but take precautions against taking in too much of the toxic brew. The beetles sever the veins of the leaves it consumes upstream of where they are eating to lessen the flow of latex to that particular area of the leaf. It seems even they have a limit to how much toxicity they can endure.

After mating, the beetles lay eggs in the base of the plant’s stem. When the eggs hatch, the resultant larvae burrow into the ground and feed on the plant’s roots, which is where they spend the winter, among the roots. In spring they create a pupation chamber, emerging as adults about a month later. This is when we see them as adults feeding on the fresh spring milkweed leaves and buds.

This insect’s Latin name is Tetraopes tetrophthalmus and refers to the beetle’s four eyes, two below the antennae and two above the antennae. tetra = four, ophthalmus = eyes.

Another beetle’s identity in the past week was not as obvious to me as was the sighting of the red milkweed beetle. This beetle’s name didn’t come to me quite as easily. I knew elm was somewhere in the name of the insect but I didn’t remember what other words went with it.

My first guess was elm leaf chafer. But no, it wasn’t a chafer at all but a leaf beetle. I’d seen this beetle before. And, after a few minutes of head scratching it came to me, a larger elm leaf beetle (Monocesta coryli).

(Yes, there is a regular elm leaf beetle (Xanthogaleruca luteola) which measures about 6 – 8 mm while the larger elm leaf beetle (Monocesta coryli) is about 10 – 16 mm long).

There were  perhaps a dozen or more of the beetles in view, which were first spotted by sharp-eyed Rangers Dakota and Molly. All of the beetles were on poison ivy.

Bears, deer and raccoons may eat the leaves and stems of poison ivy. Certain woodpeckers, crows, turkey, bobwhite and other birds eat the berries of the plant and Japanese beetles have been known to skeletonize the leaves. But, I can’t seem to find a reference stating larger elm leaf beetles munch on the foliage or have any other association with the plant. None of the beetles we witnessed were actually eating the plant, they were simply walking about on the leaves and stems.

And then it occurred to me. The beetles were simply using the poison ivy leaves as staging platforms, take-off platforms. They’ve probably freshly emerged as adults from pupation in the soil and using whatever plant leaves were available to climb on to get enough height for take-off in search of elms and other host trees to feed and lay eggs on.

The name Monocesta coryli seems to translate to “one basket hazelnut” or “hazelnut basket.” Mono = one, cesta = basket, coryli = hazel or hazelnut. The beetles do feed on hazelnut, but according to North Carolina State University they also feed on elm, dogwood, pecan, river birch, plum, and hawthorn.

You learn something every day.