I've been on the lookout for one of the many slug caterpillars that occur in this region for several years. I knew they were best looked for from August to October, and apparently were found closer to the ground, on the undersides of leaves. After turning over what seems like millions of leaves, and finding lots of interesting things, but no slug cats, today it finally happened. But they are so small (about 1 cm or less), that at first I thought this little flat thing was a gall on the basswood leaf and almost passed it by. Then I thought it looked an interesting gall and I should photograph it. And that was when I realized what I was looking at!