Probably Pleasing Fungus Beetle Exuviae on Douglas Fir in Colorado

Subject: Help Identify
Location: Colorado
April 28, 2016 1:56 pm
found these on a few mature Douglas fir.
Signature: John

Unknown Exuviae
Probably Pleasing Fungus Beetle Exuviae

Dear John,
These are the exuviae or shed exoskeletons of some unknown insect.  We will continue to research their identity.

Unknown Exuviae
Probably Pleasing Fungus Beetle Exuviae
Unknown Exuviae
Probably Pleasing Fungus Beetle Exuviae

Update May 4, 2016:  Introducing our new intern Bennett
Several weeks ago, we received an intriguing request from a local neighbor that eventually led to a meeting with our neighbor and his young science-minded son.  In his free time, Bennet will be attempting to identify the currently 444 unidentified postings in our archives.

Subject: Need Help?
Location: Los Angeles
April 27, 2016 9:33 pm
Hi Daniel,
I am a neighbor on Mt. Washington (Ave 37) and I have a science minded teenager. He’s done experiments at the Cabrillo Aquarium, won multiple medals in the LAUSD science bowl since grade 5 and was Captain of the Eagle Rock Science Olympiad team that went to the national finals in 2013. I was wondering if you ever need help or took on an intern (non-paid of course) for WtB? He wants to study entomology and I thought perhaps a project like yours would be a fun spot for him.

Here is Bennett’s first attempt at identifying a recent posting.

May 3, 2016
Hi Daniel, this is Bennett. I’m sorry for not looking into the unidentified post earlier, I had a lot of schoolwork getting in the way. Now that I spent some time looking at it and doing some research it seems to resemble some sort of carpet beetle larvae shedding. I’m not able to give a definite ID on species, and I could be wrong on this, but after doing some research it’s my best guess so far. I’ve attached 2 images that seem similar to the images the person provided, but the main difference is the lack of spikes at the tip of the tail. I hope this helps in some way.

Thanks so much for looking into this unidentified posting Bennet.  Our big doubt regarding Carpet Beetle exuviae is that the habitat seems wrong.  The exuviae are hanging from the tip of the abdomen, which is a common orientation for Lepidoptera pupae as well as Coleoptera pupae.  Our initial thought is that this was most likely one of those two orders.  We do have one request in the future:  Please provide links to images you locate in your online research rather than to attach the images.  We cannot pilfer images from another site to post them to WTB? as that would be plagiarism.  A better strategy is to link either to an outside site or even better, to link to our own archives.  We are not yet closing the book on this ID.  Searching for caterpillars or beetle larvae that feed in large numbers on Douglas Fir would be a good start.  We would also not entirely rule out that these might be Sawfly exuviae.  We believe they are pupal casings and not larval casings, indicating that the insect that left them has complete metamorphosis.

Update from Bennett:  May 23, 2016
Hi Daniel,
… I do think that I have positively identified the mystery exuviae. The images seem also identical to the exuviae of the Fungus Beetle (Gibbifer californicus), I am almost positive that it is this or another closely related species. Here is the bugguide page that contains the image that I found identical:
I hope this is accurate!

Wow Bennett,
That BugGuide posting looks like a really good visual match.  Additionally, according to BugGuide, the species is found in Colorado.  BugGuide also states “Larvae feed on wood-destroying fungi” and “female lays eggs in bark crevices of fallen rotting logs” and though the exuviae are on a branch attached to a tree, it is also possible that it could be a lower, dead branch that has fungal growth.  Of the family Erotylidae, the Pleasing Fungus Beetles, BugGuide notes:  “
larvae and adults feed on the fruiting bodies of fungi growing in decaying wood” and fungus is frequently found on living trees that are compromised.  We agree that though this might not be the exact species, it is likely something closely related.  Great job Bennett.  Thanks so much for helping us to clear up some postings that are currently Unidentified on our site one posting at a time.

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