What's That Bug? does not endorse extermination

Pebble Encased Caterpillar

Woolly Bear Mystery

Pebble Encased Caterpillar
Location:  Southwestern Montana, at about 5,000 feet in a mixed pine forest
October 10, 2010 9:48 am
Daniel:
Here is the mystery: the small and large caterpillar working together to encase the larger caterpillar in a pebble cocoon. My friend captured them in the act on a rock in a road near a campground in Western Montana in late August. The larger caterpillar began to coat itself with a sticky excretion. The smaller caterpillar climbed up and down the rock to find little pebbles, carry them to the larger caterpillar and stick them on, until the larger caterpillar was completely encased. The photographer then removed the caterpillars from the road for safety. I wrote about them in my nature column in the local newspaper, have not had any luck identifying them, and have promised my readers that I would let them know when I knew more.
We all really appreciate your help.
Signature:  Dorinda in Montana

Woolly Bear Mystery

Hi Again Dorinda,
Thanks for taking the time to resend this unusual occurrence.  We are mystified and we cannot even begin to explain what these images appear to document.  We know of no cases of Caterpillars combining forces for any such activities, nor do we know of any Tiger Moth Caterpillars, commonly called Woolly Bears, using pebbles in the construction of a cocoon.  Perhaps our readership will be able to provide something in the way of an explanation.  The pink background in the final image is curious.

Woolly Bear Mystery

The last picture had a pink background due to moving the rock out of the road to keep it safe from traffic. The friend who took the series (I’ve attached a couple of others), swears that she and her husband watched the smaller caterpillar bring the pebbles to the larger one. She was absolutely amazed. She and her husband are pretty simple folks, and love to camp out, which is when they spotted this pair. I’d really don’t believe that they staged this in any way. She actually brought the rock back with to her house in town, and put it in her garage for shelter.
As I said, I’m a writer with a nature column going on 25 years in our local newspaper, called Bird Seed, and I get told a lot of stories about birds and animals. This story was brought up casually, and took some work on my part to get the photos sent to me digitally, as they did not know how to do it. She initially showed them to me on her camera at the farmer’s market where she has a booth, and asked me if I knew what they were, or had heard of anything like it before. I sure hadn’t, but thought of you. She told me that her husband lay down in the road to take the pics with his brand new digital camera, and had to move a couple of times due to traffic.
I know that the photos are not quite good enough to show the smaller caterpillar and the pebble he is carrying clearly, but one of the pic number 4 does show that.
I really appreciate any help you can be with this little mystery.
Dorinda Troutman

Woolly Bear Mystery

Hi again Dorinda,
The new photo you included seems to chronologically fit between the final two images you sent earlier, and it does not provide any additional information regarding this mystery.  Again, hopefully our readership may provide some clues.

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What's That Bug? does not endorse extermination
Location: Montana
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