Thanks for your question.

Various of us Master Gardeners have been consulting on your question. We are of two minds.

One possibility is the pine web worm (Pococera robustella). It is common in the eastern United States and reports have been made of its sighting in Wisconsin. However there does not appear to be reports of it being found in Minnesota. See:

https://bugguide.net/node/view/1010768/bgimage

https://entnemdept.ufl.edu/creatures/trees/moths/pine_webworm.htm

https://www.fdacs.gov/content/download/10799/file/ent419.pdf

Another possibility is the White Pine Sawfly (Neodiprion sp). This does exist in Minnesota and would be consistent with your observing it on a white pine. This insect undergoes several developmental stages known as instars. Only one of these instar stages comes close to matching what you observed. See:

https://www.sawflies.org.uk/neodiprion-sertifer/

http://www.treesquad.com/sawflies

https://mastergardener.extension.wisc.edu/files/2017/04/sawflies.pdf

We apologize for not providing you a conclusive answer but only two educated guesses.

Good luck. Thanks for using our forum.