Resource Hints: How do I find out what these tree-eaters are?

Was doing some landscaping this past weekend in Chicago, as it was lovely outside.

I’ve noticed some mites (I think) on a japanese maple tree, under the bark, which is cracked here and there. They are tiny, a few millimeters in length, and white in color. They are an oblong shape, pointed at either end, like an oak leaf. They are way too small for me to photograph. They (or some other unseen pest) are chewing up the bark and depositing some sticky brown paste between the bark and the wood.

I know that some mites are good guys, and so I shouldn’t just go off and pesticide this thing, but I am concerned, because it is a handsome old tree.

Is there a well-vetted online resource for tracking down these critters, or doing some research based on the geography, the tree, and the symptoms? I’d like to poke around some on my own before I hire someone.

A local landscaper or extension service will be able to help you, if you were in Ohio I could tell you exactly who to call. Pest identification is a free service in many nursery/landscape businesses.
Here are some linkies:

And HERE is the place you can send in your bugs for identifiation:

More buggy info:

Wonderful. Thanks for the leads, Snowcarpet.