1. We learned yesterday that it is permitted to close the door or window to a house if a fly or other small insect enters because one has no control over where it flies. One may even close the door to a specific room in the house. However, trapping a fly in between a window and a screen would be problematic on a rabbinic level, since its movement is now significantly limited. The same would be true if one further traps a spider or cockroach inside a narrowly enclosed area, even if they were already previously somewhat confined. This would not constitute a Torah prohibition since, as discussed previously, insects are not considered to be animals normally trapped or hunted. If there is a small space or area through which the insect can escape, then trapping in this manner is permitted if there is a good chance that it will indeed find the opening and escape (Mishnah Berurah 316:18; The 39 Melochos, p.861).

2. We learned previously that the third condition for the Torah melachah of tzad is that the animal was not previously trapped to some degree. If it is partially trapped, fully trapping it constitutes a rabbinic prohibition. However, an animal that is already fully trapped may be placed in a cage or other enclosed area lechatchilah, since one does not cause any further trapping to take place (Orchot Shabbat 14:8). Accordingly, a fly that is already trapped inside a cup may be transferred to a different enclosed area.

Over the next two weeks, we will learn some exceptions to these rules, as well as whether they apply to common household pets.

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Dedicated by Fran Broder as a zechus for everlasting peace in Eretz Yisrael in the merit of learning Hilchos Shabbos.