The melacha of trapping is one of the 39 melachot that are forbidden from the
Torah for a Jew to perform on Shabbat. The actual definition of this melacha is
not the killing of an beast, bird, or insect, which is definitely forbidden on Shabbat,
but rather to enclose such a being in a trap.
Introduction: 3 Fundamental Concepts in Sedah
1) Need for the Animal/Insect:
All melachot that are forbidden on Shabbat, are forbidden from the Torah (medeoraita)
if one performs the melacha in the same fashion it was done during the building
of the Mishkan. This is rule will always be employed while studying Hilchot Shabbat.
During the building of the Mishkan, various animals were trapped for their skins.
Here lies an essential guide in determining whether trapping an animal will be forbidden
on the Torah-level or Rabbinic-level: if one needs the actual body of the animal/insect
(for skin or meat etc.) the transgression of trapping such an entity would be Torah-level.
If not, the transgression would be Rabbinic-level (Maran Oreh Hayim 316:3).
2) Mehousar Sedah:
Another fundamental principle of this melacha, stems from the Gemara (Shabbat 106a-106b).
For one to transgress the melacha of Sedah on a Torah-level, can only happen when
the beast, bird or insect is trapped in the trap. The term "Mehousar Sedah" is
used in the Gemara, which literally translates to as "lack of entrapment". If an
animal/insect was "Mehousar Sedah" it would be only Rabbincally forbidden (as long
as some level of trapping was achieved). However, if an animal/insect was not "Mehousar
Sedah" (meaning trapped) it would be forbidden on a Torah-level. For example, if
one encloses a fly in a house, that fly is not considered trapped at all, as one
cannot grab it with one swoop, and would thusly be permitted. However, enclosing
a deer in a house or courtyard where one could grab it in one attempt would be forbidden
on a Torah-level, for the deer is trapped in the house or courtyard. However, if
the area was large and one could not grab it with one attempt, this would only be
forbidden on a Rabbinic-level (and still not allowed because one made it easier
to trap it later; some level of trapping did take place).
3) Applies to Beasts, Birds and Insects:
And finally, the third fundamental principle in understanding the melacha of Sedah,
is that this prohibition only applies for "hayot", or beasts, birds, and insects.
However, domestic animals, (not necessarily only domesticated, but even a horse
or cow, "behemot" in Hebrew) have no prohibition surrounding them of trapping.
In addition, beasts or birds that are domesticated have no prohibition of trapping
as well. However, this can change if the animal revolts and essentially acts like
a "wild" animal. More on this later.