River Birch infestation
I had some catepillar-type bug eating many leaves on my River Birch (mostly in June). Maybe 5% of the leaves eaten mostly on the lower branches. See attached photo.
Would like to know what it is and how to best prevent reoccurance.
This looks like the larvae of dusky birch sawfly. (They are not caterpillars.) They like to congregate and consume leaves, but usually do not do significant damage to large or established trees. Since they are so gregarious, it is easy to mechanically (i.e. using gloves hands) pull them off. Drop them in a bucket of soapy water to drown. When small, the larvae can be sprayed with horticultural oil, but that is usually more much labor intensive.
Here is info about sawflies: https://extension.umd.edu/hgic/topics/sawflies-trees-and-shrubs
Be mindful that trees grow many more leaves than they actually need. Losing some is not a problem. Also, larvae like this (and caterpillars, too) are a big food source for birds.