Last week I wrote about how my son and I had chanced upon slugs eating a dead earthworm in our backyard. The following nite we decided to reproduce our observations by actually offering earthworms to slugs. During the afternoon we went out and collected dead earthworms from the sidewalks—casualties left from the morning’s rain. A brief soak in a solution of trisodium phosphate, followed by a water rinse, restored, not their lives, but their plumpness.
Later in the backyard around 9 pm, the first slug we saw was a large Arion subfuscus. I placed one intact “reconstituted” worm a few centimeters in front of it. A minute later, the slug had already contacted the worm and was starting to eat it.
Soon the slug had literally chopped the worm into smaller pieces and was consuming each one slowly.
I don’t know how often these slugs get a chance to eat dead earthworms and other animal matter in the wild. But I have just thought of a way this question can be answered easily. In a previous post, I mentioned how I had determined the diet of the land snail Oxyloma retusa from the microscopic examinations of its feces. The feces of slugs should also reveal what they normally eat. Earthworm flesh, once it has gone thru a slug’s stomach and intestine, would probably be difficult to identify. But, I am almost certain that the tiny hairs (setae) that cover an earthworm's outer skin will survive intact slugs’ digestive processes and can be identified in their feces.
That will be the next weekend’s project.