Forbidden and Permitted Trapping on Shabbos (Part I)
If a bird flies into the house and a window, a second door
or skylight is open through which it could escape, there is no issue of
trapping it and the door may be locked. Otherwise, it is forbidden. If the
room is small, it is forbidden by the Torah. If it is large, it is forbidden
by the rabbis. Therefore, if the room is large and leaving the door open would
cause discomfort in cold weather—or for any other reason—it is permitted to
close the door. But if the room is small, so that the bird could be readily
caught, it is forbidden.
If flies, mosquitoes etc. are in a container, it is
permitted by the Torah to close it. Since these are not species that are
ordinarily trapped , the prohibition of trapping does not apply to them. But
the rabbis forbid trapping even insects. Nevertheless, the container can be
closed if an opening is left through which they can escape.
If there are flies or mosquitoes in a small container and a
person wants to close it completely, he should blow into it so that he
scatters the insects that he sees. Once he does that, he does not have to
check to see if there are any more of them because the issue involves a doubt
in a psik raysha pertaining to a rabbinical prohibition. If there is
food in the container, the matter is even clearer because he would certainly
prefer that no insects remained in the container.