Among the items eaten by a slug from my backyard that was the subject of this post were some pollen that I had not bothered to identify when I was writing that post. A reader indicated that the pollen were the type made by pine and fir trees. There are indeed 3 large eastern white pine (Pinus strobus) trees in our backyard. Until about 2 weeks ago there were layers of their yellow pollen accumulating at various spots in the backyard.
But I wanted to confirm that the pollen from the pine trees did look like those from the slug's feces. So, yesterday I got some pollen from one of the trees and examined them under the microscope. Morphologically and dimensionally, they matched the pollen that I had observed in the slug's feces. Since there was so much pollen around that it is not surprising that the slug had eaten some. Whether or not they can digest the pollen is another question.
The pollen of the eastern white pine. They are actually yellow. The pollen on the right was 56 µm across. The pictures were taken with a light microscope.