Are those really slugs on the leaves? No. Caterpillars?
No. Pear sawflies, also known as pear slugs or cherry
sawflies, are out and feeding in the North Willamette Valley.
The are the larvae of small wasps. They have been spotted on
cherry but have other common hosts including pears and plums.
Look for them on the lower leaves of host plants. I've put together
a new pear sawfly page with more information, links, and images.