Hello,

I can’t see this insect clearly in the pictures. Were they actually moving about or completely still?

If still, they are likely the pupa of a moth or beetle and are no longer feeding. If they are crawling about then they may still be feeding.

If you can, save one or two that seem to be undamaged and in  good condition in a jar or dry baggie. Place in the freezer and save for an arborist to identify.

You can get an identification and a tree health assessment by hiring a professional to come on site and go over all the tree’s issues. This  tree has an older injury to the trunk to which the insects are attracted.  The trunk should be examined to see if rot has set in. The root zone and the crown of the tree should be evaluated, too.

You can hire a certified arborist, a professional who has taken training in care, diseases, pests and passed certification tests. He/she will come on site and give a complete diagnosis and a plant care plan. Find certified arborists by zip code here—-

www.treesaregood.org

MSU Diagnostics can identify an insect sample in good condition  that you mail in, but you wouldn’t receive a full evaluation of the other possible issues the tree has. To submit insects for ID, submit insects in a small leak proof vial filled with rubbing alcohol or white vinegar (the postal service prefers you send them in vinegar). Place the vial in a small zip-lock baggie, then in a small box or mailing tube and mail to

Diagnostic Services

578 Wilson Rd.

East Lansing MI 48824-6469

Be sure to include a note with your contact information including your email address.

You can download one of our submittal forms here:

https://pestid.msu.edu/wp-content/uploads/2017/04/MSU-DS-Form-012-001-version-2.0.pdf

Here are a couple possibilities( there are several others)

Oakworm pupa-

https://bugguide.net/node/view/7295

Red oak clearwing borer-

https://content.ces.ncsu.edu/red-oak-clearwing-borer

If you can get a clear, in focus, shot of a couple on a plain sheet of paper in good light, please attach here and I will try to identify them for you.

Tap the photo below to see examples of oakworm pupa

I still can’t see enough details to identify the insect.

But because you say it is fast moving and skinny, it is likely a centipede of some sort, which like to live and hunt insects in moist dark crevices. If it is a centipede, there is no need to kill it because it is hunting insects and does not damage wood or trees. 

https://oepos.ca.uky.edu/content/house-centipede

You may try to catch one in a closed container, in good condition, and chill  in a refrigerator for several hours to slow it down( and so take clear pictures). Be sure to wear gloves as some insects may bite when handled, or sting with long hairs that irritate the skin.

I will forward your query to MSU’s entomologist for an opinion on the insect and the empty pupal cases.  This may take a few days to get a response at this busy time of year. I will add his reply to your question thread, and you will be notified when that update occurs. Thank you for your patience.