Spot the Beetle

A few weeks ago, as we continued to explore areas in our new community, we stopped by a little wayside between Duvall and Carnation called Chinook Bend Natural Area.

We'd popped in there last summer and attempted to go for a walk but were felled by the heat within five minutes, as the path took us through a treeless swale and, after 25 years of living in the Puget Sound region, we were no longer capable of surviving outside a narrow temperature range.

This time, however, it was a gentle, early-spring day with a light breeze, so we made it to the river, over a pile of slash, into a woodland, and back again.

Along the way we encountered this marvelous beetle (at left).

Most western gardeners would probably not call this a marvelous beetle. They would call it many rude names. Because it is a western spotted cucumber beetle, Diabrotica undecimpunctata. 

No sources have much good to say about this beetle. Most of the sources are ones dealing with pest management, and they point out that this insect transmits crop diseases and damages a wide variety of garden plants and crops, including corn, soy, squash, and cucumbers.

Even the Audubon field guide says (of its eastern cousin) that it's "one of the most destructive beetles" and "damages foliage, flowers, and pollen of cucumbers, melons, corn, potatoes, and peanuts." Its offspring are called "corn rootworms" because they feed on the roots of crops.

I would surely pluck this beetle off my vegetables if I found it in our garden, but this beetle was minding its own business and trundling around in its native habitat, ignorant of the fact that it was named after a vegetable (actually, a fruit) that itself is native to southeast Asia.

The plant it's on appears to be a Sitka willow, Salix sitchensis. Part of what made this insect so marvelous to us was its cartoonish pattern of big black spots on a bright green background, but also the way that ridiculous coloration caused it to blend in with the catkins, which appeared black-spotted thanks to the dark bracts at the base of its small flowers.

What the beetle's nefarious plans were after we left, I cannot say, though from what I could dig up on its life history, it'll include laying up to 300 eggs over the next few weeks, if it's a female. For now, it was busy doing just what the field guide Insects of the Pacific Northwest said it usually does: "feeding on light-colored flowers." Apparently it's fond of dandelions.

It was a lot easier to find admiring commentary on the willow, which was used by native peoples for a variety of purposes--making ropes, gray pigment for dyeing mountain-goat wool, and even absorbent material for diapers. It'd be interesting to know what Native Americans thought of the beetle in those times, as I assume it wasn't a major agricultural pest back in the day.

I couldn't figure out the meaning of the first half of its scientific name, but the undecimpunctata part means "11-spotted." A curious name for a 12-spotted beetle, except that two of the spots come together to form one big spot when it closes its wing covers. Tricky beast.