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Shabbat Parashat Shelach| 5770

Ask the Rabbi: problem with moths on Shabbat

Question: We have had problems in the past with moths in a certain closet, and so we have put a material that kills moths and their larvae by fumes that are trapped and accumulate inside. If we open the door, may we close it again on Shabbat, or is that considered killing the moths?


Answer: Your question is affected by many halachic concepts, including some that are too complicated to resolve in this context, but we will be able to give you a final ruling for this case.

It is forbidden to kill animal life on Shabbat, and this is even more severe than the prohibition to trap them (Shulchan Aruch, Orach Chayim 316:9). Yet, there are several potential reasons for leniency. We are assuming that your main intention in closing the door is unrelated to moths or to keep the smell out of the room. (Experts question the safety of moth balls, which are toxic and probably carcinogenic; this may be sufficient reason not to use them, at least without precautions. Hopefully you have a safer material.) There is sufficient time to kill the moths, larvae (developing moths), and/or eggs during the week.

If it is clear that closing the door will kill moths, this unintentional but definite and otherwise desired violation of Shabbat is called a p’sik reishei (=pr), which is usually forbidden from the Torah (Shabbat 75a). On the other hand, the manner in which the killing happens is not a classic action. Rather, one puts out poison, which later kills. There is a machloket Acharonim whether one is allowed to put poison in front of animal on Shabbat so that it will eat it and die. The Shvut Yaakov (II, 45) makes a strong argument that it is gerama (indirect causation), which can be permitted with other alleviating factors. Here, the killing is a melacha she’eina tzricha l’gufa (it is not done to make use of the final result, i.e., the dead moth), which almost all Rishonim agree is only a rabbinic prohibition. The Shvut Yaakov says that it can be permitted to avoid tza’ar (and likely, similarly, a loss). Even in the case of a pr of a direct but unintentional action, significant opinions permit the matter if only a rabbinic prohibition is involved (Terumat Hadeshen 64; see Yabia Omer I, OC 19). 

Our case, though, is different in the directions of both stringency and leniency. Here, the moths are not enticed to eat the poison, but rather the fumes reach the moths, which is more direct (Yabia Omer, OC III, 20 makes this distinction regarding a case of spraying). On the other hand, here the substance is placed before Shabbat, and that which you are inquiring about is closing a door on Shabbat. This does not create the fumes but stops them from dissipating. In a parallel case, when one closes a pot of not yet cooked food so that the heat will not escape and the food will cook faster, most consider this a full violation. On the other hand, it is unclear that this model should be applied in all contexts. (The matter needs further investigation beyond our present scope).

The strongest grounds for permitting this is the uncertainty whether any moths will die on Shabbat as a result of closing the doors. First there is the question whether there are any moths or larvae there at this time, especially after using the substance over time. That might already make it considered a davar she’eino mitkaven, not a certainty that a forbidden status will be reached, which is permitted. There is major discussion whether this leniency applies even when the uncertainty has to do with an existing situation (i.e., are there moths?) (see Taz, OC 316:3) or whether if there is a pr assuming there are moths, this is a pr and forbidden. Furthermore, our research suggests that it is probably not clear if moths that are there will definitely die on Shabbat because the extermination process is a slow one. Therefore, assuming that the reason to close the door is not primarily to kill the moths as quickly as possible, it should be permitted.

In summary, because of a few possible factors and perhaps their confluence, it should be permitted to close the door.

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