Short answer. Not automatically. The original owner has the right to pursue the swarm onto your land and reclaim it, though they must pay you for any damage the pursuit causes. Only if the owner never pursues the swarm, or stops chasing it within two consecutive days, may you occupy and keep it as the possessor.
What the law says
The owner of a swarm of bees shall have a right to pursue them to another's land, indemnifying the possessor of the latter for the damage. If the owner has not pursued the swarm, or ceases to do so within two consecutive days, the possessor of the land may occupy or retain the same.
Civil Code, Article 716 — Bees And Domesticated Animals. Read the full provision →
The bee owner keeps a right to pursue and reclaim
Article 716 gives the original owner of a swarm of bees a real right to chase it onto someone else's land and take it back — losing the bees to your property is not, by itself, enough to lose ownership of them. That pursuit right does come with a cost to the owner: they must indemnify the possessor of your land for any damage the pursuit causes.
The two-day window is what actually matters to you
Your right to the swarm turns on the owner's conduct within a fixed window. If the owner has not pursued the swarm, or begins pursuing but ceases to do so within two consecutive days, the article lets you, as the possessor of the land, occupy or retain the bees yourself. Before that window closes, the swarm is still legally the pursuing owner's to reclaim.
Why the law treats bees this way
Bees move on their own and can end up anywhere, so the law needs a clear cutoff for when an owner's claim lapses. Two consecutive days of inaction is that cutoff — short enough that a landowner is not stuck indefinitely wondering whether a swarm on their property is claimed, but long enough to give a genuinely interested owner a real chance to come get it.
The indemnity is separate from who ends up with the bees
Even where the owner successfully pursues and reclaims the swarm within the two-day window, Article 716 still requires them to indemnify you for whatever damage that pursuit caused to your land or property. Recovering the bees and owing compensation for the pursuit are two separate consequences under this article, and the first does not cancel out the second, regardless of how the pursuit itself unfolded on your land.
Other stray domesticated animals get a longer window, not the same one
Article 716 does not stop at bees. It also covers other domesticated animals that end up in someone else's keeping, but on different terms: the owner of domesticated animals may also claim them within twenty days to be counted from their occupation by another person, and only once this period having expired do they belong to whoever has caught and kept them. Twenty days is considerably longer than the two-day window for bees, so do not assume the timeline that applies to a swarm also governs a stray domesticated animal that wanders onto your land.