Hello,

There are many insects that munch on American Linden/Basswood (Tilia americana) including cankerworms, forest tent caterpillar, linden looper, tussock moth, Japanese beetles and other caterpillars. Read more here: https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=287365&isprofile=1&adv=Linden

And here: https://apps.extension.umn.edu/garden/diagnose/plant/deciduous/linden/leavesholes.html

The foam may be caused by a spittlebug which does not otherwise harm the leaf. Read more here: https://hort.extension.wisc.edu/articles/spittlebugs/

It would appear that many creatures are at work on your tree. In order to obtain a more thorough diagnosis, submit the pictures and a sample to MSU Extension’s Plant and Pest Diagnostic Lab at: https://www.canr.msu.edu/pestid/

A certified arborist would be able to assess your trees to find one in your area, go to: www.treesaregood.org, the website of the International Society of Arboriculture.

Thank you for contacting Ask Extension.