Sand Dune Mystery from Idaho may be Rubber Boa

Family Mystery
Location: Sand Dunes, Southeast Idaho, Fremont County, east of Saint Anthony
June 7, 2011 11:08 pm
This photo was taken in 1984 at the Sand Dunes in Southeast Idaho, Fremont County. I watched for 15-20 minutes while this . . . thing made this pattern in the sand. It would scoop up a pile of sand, push it out in the fan/petal shape, scoop up a pile of sand, push it out . . . I have recently re-engaged in my quest to find out what I was watching.
Any ideas what it is?
Signature: Bug Lover’s Cousin

Sand Dune Mystery from Idaho

Dear Bug Lover’s Cousin,
We have no idea what this creature is and we would love to help you solve this more than 25 year old mystery.  We do not believe this is an insect.  You did not indicate the size of the creature.  We are more inclined to believe it is reptilian than one of the arthropods, but that is pure speculation.  We are boarding a plane in a few hours and we will be out of the office for a week, and during that time we will not be checking emails, so we will not be able to provide any further assistance until we return.  Our regular readership will be able to post updates to this posting, however, any new readers will need to wait until next week to have their comments approved.  We hope we are eventually able to provide you with an identification.

Going on my 25 year old memory of this thing I will venture – it was:
maybe 2-4 inches long (not positive I EVER saw the end of it but I think I did)
about 2-2.5 inches circumference
entirely black except for the tip (head?) which was reddish
I saw no legs or mouth
it moved like a worm or caterpillar (a larvae?)
didn’t seem to be ingesting anything, just kept making the pattern
My brother was with me at the time and agrees with this description
Enjoy your time out of the office, I look forward to any info/guesses you might have.
Thank you.

Karl provides an alternate possibility:  White Lined Sphinx
October 26, 2011
Hi Daniel and Bug Lover’s Cousin:
It is a little hard to tell from the photo but based on what is visible and your description I suspect that this is a large caterpillar. There are a number of species that burrow into soft soil or sand to pupate. I suggest that a good candidate would be a White-Lined Sphinx (Hyles lineata). Caterpillars of the species show considerable color variation but are generally striped or mottled green and black, and orange or reddish caudal horns and/or head capsules are quite common (to me it looks like it may be showing a horn). You could check out this interesting video to see if the behavior looks familiar. Here is another image from the Bugguide site. Regards. Karl

Thanks Karl for your alternative possibility.

5 thoughts on “Sand Dune Mystery from Idaho may be Rubber Boa”

  1. Amateur herpetologist here–I suspect this may be a rubber boa. They are burrowing snakes with a red-tipped tail that they often use to confuse predators (head-like motion, and even false strikes). Though the picture resolution isn’t very high, the bluntness of the tail indicates it may have been attacked repeatedly. Great photo/info page at

  2. What can I say; it’s possible. With size being unknown we have to go with color and other features. I checked out the photos on the Rubber Boas site above, posted by CB. They don’t seem right. It was much darker, the red was much redder, it had bumps – like a catepillar. (If it WAS a Rubber Boa, why was it making that pattern in the sand?) I’m not crossing the Rubber Boa off my list, I just want to know for sure. Thanks, CB, for your input. If you find anything else I’d love to see/hear it. Thanks bugman!

  3. I AM the Bug Lover’s Cousin. Over these past few years we have made several trips out to this same location, the St. Anthony Sand Dunes, and have yet to see this creature or this pattern again. General consensus, from this and other sites, is that this is a Rubber Boa. So I’ll go with that possibility as I continue my search. Any other thoughts or ideas would be appreciated!

    • Thanks for the update. It is not unusual for us to get an identification comment as many as ten years after a posting is made, so there is still a chance someone may provide additional information, but since the first comment came from a someone very familiar with snakes, we are inclined to agree, though we also agree with Karl that a Sphinx Caterpillar might be the culprit. The Bedstraw Hawkmoth Caterpillar fits the general description your cousin provided and it is reported in the states and Canadian provinces bordering Idaho. This image of a Whitelined Sphinx Caterpillar in the sand from BugGuide documents the behavior of caterpillars in the genus. The one consideration causing us to continue to favor the Rubber Boa theory is that it was observed for such a long time, and we suspect a Caterpillar would have buried itself much quicker.


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