Green Immigrant Leaf Weevil

2009 November 7

This beetle was photographed back in August. I’m not sure whether to classify this as a “found in house” or “found in yard”, because this particular one was hanging out on the doorjam and was most likely trying to get in when it died there. Most summers, we get significant eruptions of them, although this year they were not as common as they have been in the past.

Aside from the color, they are generally similar to the Clover weevils that are also pretty common around here, with the blunt, short snouts and the armored wing covers that wrap quite a way around the abdomen.


There are several kinds of green weevils, but I’m pretty sure that this one is a Green Immigrant Leaf Weevil, Polydrusus sericius, because they have bigger eyes than the other kinds of green weevils, and more pronounced dark lines on the wing covers.



As you have probably guessed from the common name, this is yet another non-native species that has only reached the area recently. I don’t remember seeing them when I was a kid, so they’ve probably just arrived in Michigan within the last 30 years, and they are now widespread in North America, just like they have been all along in Europe (and probably Asia)[1]. Bug Guide says that they eat yellow birch. This is a North American tree, though, so it wouldn’t have been available to them back home in Europe. Other sources say that they also like poplar and apple. All of these trees are common here, so I expect that they eat well. In spite of their large numbers sometimes, they aren’t often that serious of a plant pest because they just take small notches out of the edges of leaves. They sometimes get into houses enough to be considered a nuisance, though. If they do need to be controlled, they can be treated similarly to other weevils.

[1] When one looks at a map of the Northern Hemisphere, it is obvious that the main reason most of these cold-tolerant creatures hadn’t reached North America a long time ago is the Bering Strait. The thing is, the Bering Strait is pretty shallow, and there really isn’t any fundamental reason why it should be submerged (and at times in the not-wildly-distant past, there was enough water tied up in glaciers that it wasn’t submerged, which is how people got here. Most of the bugs probably wouldn have followed us if it hadn’t been an arctic mostly-glaciated wasteland at the time). For a long time, I’d assumed that the reason there was a Bering Strait was because it was the margin between the North American Plate and the Eurasian Plate. But, in the course of a discussion about whether it would ever be practical to build a bridge from Alaska to Siberia, we found out that a big chunk of Siberia is actually on the North American Plate! So, the Bering Strait isn’t a plate boundary at all, it’s just a low spot on what is really just a projection from Alaska all the way over to the Chersky Range. If the land in the Bering Strait area had been uplifted just a bit in the past, (or if the Earth had just a bit less water to start with), North America and Asia would have had a permanent land bridge, and all these little bugs would have been here all along.

4 Responses
  1. November 12, 2009

    Are the little green dots scales or fuzz?

  2. November 13, 2009

    I think they’re scales, although they do seem to stick up a bit. The description on Bug Guide calls them scales, so I guess I can go along with that.

  3. Della3 permalink
    February 25, 2010

    Turn the photo of the abdomen a quarter turn clockwise and you have an aboriginal drawing of a face!

  4. February 25, 2010

    Say, it *does* look like a face, particularly the way the legs look like a 3d nose! And three mouths, but hey, you can’t have everything.

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