Goldsmith Beetle from Agate Beach

2015 August 1

We were down at Agate Beach (at the northeast end of Misery Bay)[1] on June 14, 2015, when Rosie found this excellent scarab beetle crawling around on the stones.

It looks like a Goldsmith Beetle, Cotalpa lanigera, the only beetle like this that lives in the eastern US. You can click on this next picture to see it full-sized, if you like.

While this one was on the beach, it probably actually came from the woods growing next to the beach, since the adult beetles eat leaves off of a lot of our common deciduous forest trees like oak, poplar, maple, and willow.

These are really pretty beetles, with not only the greenish-gold wing covers, but also iridescent green on the legs and a lot of the underbody.

The scimitar-like front legs look pretty threatening, but actually aren’t dangerous. At least, none of us were injured by it.

Goldsmith beetles are considered to be “uncommon”, and this was the first one that I’d ever seen. At least, until Rosie found another one on the beach that was dead (I didn’t photograph that one, because it wasn’t all that photogenic). Evidently, they are at least common on that particular stretch of beach.

[1] I have yet to find anyone who knows for sure whether there was a particular event that lead it to be named “Misery Bay”, although I can make a rough guess at what happened. While it is a fine beach in the summer, it is on the west side of the Keeweenaw Peninsula, which means that the winter gales off of Lake Superior hit it full force. If one tried to get through the winter in this bay, it would be miserable indeed[2]. Agate Beach in particular gets scoured so heavily by the winter storms and ice that it is mostly coarse gravel, with the sand washed away. This is incidentally also why it is a good place to look for Lake Superior Agates. The constant abuse of the rocks breaks the agates out of the rock vesicles that they formed in, and throws them up on the beach where they can be found.

[2] Then again, whoever named it might have been there at the height of black fly season, which is also pretty apalling.

7 Responses
  1. August 1, 2015

    Is that hair on the beetle’s underside, cilia, or some other structure?

  2. August 3, 2015

    Anne: The easy answer is just to say that it’s “hair”, because it looks and feels a lot like mammal hair. But then, when you start getting into it, they aren’t really the same as hair at all. They are made out of chitin instead of keratin, they grow up through the “skin” (exoskeleton) instead of being embedded in it, and they are mostly connected to nerve endings to provide a sense of touch. And, they are also more likely to be more like defensive quills than an insulating blanket like mammals have. So, technically, they are “setae”, not hair.

  3. Katbird permalink
    August 4, 2015

    I saw a similar beetle last week in Maryland- pale green on top and iridescent green on the underside- but not so hairy. Anyone know?

  4. August 5, 2015

    Insect “hair” tends to be brittle and can get rubbed off pretty easily, so it may just have been an older specimen that had lost some of its hair. Then again, it could be a regional variation – I went to BugGuide to look at pictures of this beetle species from Maryland and New Jersey, and they looked distinctly greener, and while none of them were shots of the underside, they didn’t look as hairy, either.

    (If you go to a species page on BugGuide and click on the “Data” tab, there is a table under the range map showing occurrences by state and by month. You can click in this table to get specimens just from a particular state)

  5. August 6, 2015

    The hair is made of chitin? Amazing!

  6. August 6, 2015

    Wow, very nice iridescent color on the ventral side, a very cool specimen! How close was it to the tide line?

  7. August 7, 2015

    Thanks, Justin. It was fairly close to the waterline, maybe 4 to 6 feet. Of course, there is no discernable tide on Lake Superior, and the waves were minimal that day, so even this close to the water the beach was pretty dry.

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