Monthly Mystery #6: Manzanita Scrapings

A few weeks ago I was sent the photos below, with these comments:

I found it on the bark of manzanita (Arctostaphylos) in Napa County, California on March 31. . . It resembles feeding sign of a rabbit because the scrapes go down to the cambium, but is in horizontal rows and goes too high up on the branches. It has no clear incisor marks either. I know some insects tunnel through the bark of trees and shrubs, but this looked like scrapes from a chisel or nail. The scrapes were about 1/8th inch wide, parallel, horizontal, varying lengths, and sometimes left short strips of bark hanging off the ends.  

manzanita_bug_3

manzanita_bug_2

manzanita_bug

My response was: “If this is an insect sign, the closest thing I can think of is nest material collecting by paper wasps, hornets, etc., but in my experience they always strip parallel to the grain of the wood and use weathered wood rather than fresh bark.  Also I have never seen so much stripping so close together.  I’ve seen nest material gathering by squirrels, mice, etc. that looked superficially similar, but as you pointed out there don’t seem to be any incisor marks.”  Anybody out there have any further insights?

About Charley Eiseman

I am a freelance naturalist, endlessly fascinated by the interconnections of all the living and nonliving things around me. I am the lead author of Tracks & Sign of Insects and Other Invertebrates (Stackpole Books, 2010), and continue to collect photographs and information on this subject. These days I am especially drawn to galls, leaf mines, and other plant-insect interactions.
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6 Responses to Monthly Mystery #6: Manzanita Scrapings

  1. Tim Eisele says:

    Well, if this was in an area where children pass by, I wouldn’t discount the possibility that it was, in fact, done with a nail or other small scraper. Kids do that sort of thing sometimes (at least, I did).

    • Always good to keep that possibility in mind, but I would be surprised if a kid vandalizing a shrub produced this pattern of precise, parallel, horizontal lines.

      • William Holz says:

        Yeah, that looks pretty darn focused for a kid!

        I couldn’t tell but in the first picture where the tree had a groove in it, did the lines ‘skip’, like they would if a person was scratching the bark?

        I was leaning drunk wasp at first, but that’s not really an option. 🙂

  2. Sue Cloutier says:

    A great mystery!

  3. Pingback: More Manzanita Markings | BugTracks

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