What you are seeing are the larvae of the cherry sawfly. While the damage looks bad, it rarely comes before the c herries are harvevstedand thus fruit quality is not affected by the loss of leaf area. A heavy infestation on a young tree could slow down the growth and might warrant spraying but rarely is that true on a larger tree. I generally don't recommend that they be controlled on older trees and/or trees that have finished fruiting. It can move to pears which aren't done fruiting. But there are birds that like these things and other insects as well and the life cycle as the "slug" is short so again, it is marginal whether a spray is necessary. Here is a link to the insect from our PNW Insect Handbook: https://pnwhandbooks.org/insect/tree-fruit/cherry/cherry-cherry-slug-pear-slug-cherry-sawfly-pear-sa... 

The products that probably are most useful for homeowners on this insect are the ones that contain spinosad as the active ingredient.  If you have questions about where to find it in Columbia County, give me a call at<personal data hidden> or email me at <personal data hidden>.    Chip Bubl  OSU Extension Agent/Columbia County