Uktzin, Chapter 3, Mishnah 11. Our mishnah takes up a single question about a beehive, and from that one question three separate areas of halachah unfold. A beehive is not truly planted in the earth, yet it settles into its spot and becomes fixed there until someone comes and pulls it up. Is such an object legally treated as part of the ground, or as a movable article?
Rebbi Eliezer: the beehive is like land
The Mishnah opens: "kaveres devorim", a hive of bees. Rebbi Eliezer omer harei hu kekarka - Rebbi Eliezer holds that it has the status of something joined to the ground. Three consequences follow.
"Vekosvin aleha prozbul." Its owner may rely on it in order to draw up a prozbul. Maseches Shevi'is teaches that Hillel established this enactment. Normally a debt owed to a private individual is wiped out once the shemittah year passes. Hillel's remedy was for the creditor to sign a document assigning the debt over to the court, and once the claim belongs to beis din rather than to him personally, he is able to collect after shemittah as well. There is a condition, though: only someone who holds real estate may make use of a prozbul. Rebbi Eliezer, who treats the hive as ground, therefore counts its owner as a landholder, and such a person may indeed have a prozbul drawn up for him.
"Ve'einah mekabeles tumah bimkomah." While it is standing in the place where the bees settled and built, it cannot receive tumah, because whatever is joined to the ground is not mekabel tumah.
"Veharodeh mimenah beShabbos chayav chatas." One who extracts honey from it on Shabbos is liable to bring a chatas, exactly as with the melachah of tolesh, detaching something from its place of growth, no different in principle from plucking an apple off a tree.
The Chachamim: the beehive is not like land
"Vachachamim omrim" - the Sages disagree on all counts. First, "einah kekarka", it does not have the status of land. Second, "ve'ein kosvin aleha prozbul", since it lacks the halachah of karka, ownership of a beehive is not the possession of land and no prozbul may be written upon it. Third, "umekabeles tumah bimkomah", it is an article that can receive tumah even where it stands, precisely because it is not attached to the ground. And fourth, "veharodeh mimenah beShabbos patur", one who removes a piece of honeycomb from it on Shabbos is exempt, since this is not reckoned as the melachah of tolesh.
A word on how the hive sits
It is worth noting the kind of attachment we are speaking about. The beehive is held in place with some mud, and that is all: it is not cemented into the earth. Were it fastened down with cement, that would clearly be a separate question altogether, since there we might well begin to regard it differently.
So a small wooden hive full of bees turns out to sit at the crossroads of shemittah, tumah and Shabbos, and the entire dispute rests on one deceptively simple point: when is something "attached to the ground"?