One may not own or keep a pet that disturbs the neighbors. Thus, one may not have a dangerous dog, including a dog likely to frighten people or children who pass by the owner’s yard. One may also not have a dog whose barking disturbs the neighbors’ rest. Even if a dog is trained, poses no real danger of attack, and does not bark in a way that disturbs the neighbors, it may not be kept where passersby who do not know the dog will be frightened when it barks. One may keep such a dog only when passersby are not afraid of it – for example, when it is secured with iron chains or kept behind a fence, so that everyone can see it cannot attack. In remote areas, where there is a security need, intimidating guard dogs may be allowed to patrol at night to protect the settlement, provided they do not endanger the residents. Dogs that do not frighten people at all, whether because they are especially friendly or because the local residents are used to them, do not need to be restrained (Bava Kamma 79b–80a; SA ḤM 409:3).
If a person sees a snake or scorpion in a place where people walk, there is a mitzva to kill it before it harms anyone. The same applies to a lion, wolf, or leopard roaming in a populated area. If, however, a predatory animal or venomous snake is kept in a secure enclosure where it cannot harm anyone, it should not be harmed. However, if the owner fails to guard the animal properly and the situation becomes dangerous, the owner must kill it. If the owner does not do so, anyone may kill the animal in order to protect himself and the public from danger (Tosafot, Bava Kamma 16b, s.v. Rabbi, according to Rabbeinu Tam’s explanation; Noda BiYehuda Tinyana, YD 10).
One may also kill mice and rats that damage one’s fields or enter one’s home (Mishna, Mo’ed Katan 6b). The same applies to insects and other pests in fields or homes, since they harm people (Radvaz 2:727). Moreover, the main prohibition of tza’ar ba’alei ḥayim does not apply to creatures of this sort in the same way, as their brains and nervous systems are very simple and their experience of pain and suffering is very weak. Although it is an act of piety to avoid harming any living creature needlessly, when pests cause damage, one may kill them; refraining from doing so is not an act of piety.
The same is true of ants, flies, and other insects that enter the home and interfere with its cleanliness. Although one should be careful not to harm any living creature needlessly, even of a lowly species, when such creatures bother a person, one may kill them without compromising that piety. The cleanliness and dignity of a person’s home take precedence.[8]
