A Synopsis of What We Have Learned Thus Far
Yesterday, we have explained that one may place an animal onto grass on Shabbat in order to let it graze there. Although the animal will be detaching grass from the ground, since this action is not connected to the individual at all, it is permissible.
The Poskim explain this matter two different ways. The Even Ha’Ozer writes that the primary factor regarding the laws of Shabbat is one’s intention. Thus, since the individual placing the animal on the grass does not intend for the actual forbidden work of detaching grass to come about; rather, one only wishes for the animal to eat. Thus, this forbidden work has no correlation to the individual.
On the other hand, the Bet Meir explains that the determining factor regarding the laws of Shabbat is the performance of the forbidden work through the individual’s toil. However, we are not concerned about a forbidden work that is performed on its own without the individual’s participation (although it is forbidden for one to have work done for him on Shabbat through an animal).
The Connection to Our Scenario
Let is now discuss the association between the above and our case. According to the Even Ha’Ozer who writes that the Torah is concerned about the individual’s intent while the forbidden work is being performed, it would be forbidden to put out or spray poison against pests on Shabbat since one’s intention is to kill these pests, which is a forbidden work on Shabbat.
According to the Bet Meir, on the other hand, who writes that as long as the individual is not performing the forbidden work on his own on Shabbat, there is no prohibition, it will be permissible to put out poison on Shabbat, for the pests will come to eat it on their own and die.
Halachically speaking, after deeply analyzing the words of the Poskim regarding this law, Maran Rabbeinu Ovadia Yosef zt”l rules that one may put out poison against mice and other pests on Shabbat in order for these pests to eat the poison and die. However, spraying poison directly onto pests is certainly forbidden on Shabbat.
It is therefore permissible to spray poison against pests as long as they have a way to escape (i.e. if the window is open) and one does not spray it directly on them since it is not certain that they will die as a result. However, spraying directly on them which will certainly kill them is forbidden on Shabbat. (See Responsa Yabia Omer, Volume 3, Chapter 20 and Chazon Ovadia-Shabbat, Volume 5, page 112 and on.)