Answer:
A mighty weapon in the war against winged household pests.
Face with a tree, skin like the sea. A great beast I am. Yet vermin frightens me.
In we go, out we go. All around and in a row. Always, always steady flow. When we'll stop, you'll never known. In we go, out we go.
Sleeping during the day, I hide away. Watchful through the night, I open at dawn's light. But only for the briefest time, do I shine. And then I hide away. And sleep through the day.
An open ended barrel, it is shaped like a hive. It is filled with the flesh, and the flesh is alive!
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.