Killing bugs on שבת

One who traps a deer, or any living creature, and one who slaughters it, and one who flays it, and one who salts its hide, a step in the tanning process, and one who tans its hide, and one who smooths it, removing hairs and veins, and one who cuts it into measured parts.

One who slaughters is liable. And not only slaughtering; but anyone who takes the life of one of all the types of animals, beasts, birds, fish or swarming animals – whether by slaughtering, stabbing or hitting – is liable. One who strangles a living thing until it dies is surely [doing] a subcategory of slaughtering. Hence if he lifts a fish out of a pail of water and leaves it until it dies, he is liable. And not [even] from when it dies, but once [the size of a] sela coin has dried up between its gills, he is liable – as it can no longer live. If he extended his hand into the innards of a beast and dislocates a fetus in its innards, he is liable.

We learned in the mishna: And one who traps other abominations is exempt. The Gemara infers: If one kills them he is liable. The Gemara asks: Who is the tanna who holds this opinion? Rabbi Yirmeya said: It is the opinion of Rabbi Eliezer, as it was taught in a baraita that Rabbi Eliezer says: One who kills lice on Shabbat is akin to one who kills a camel on Shabbat. Apparently, he is the Sage who holds that one is liable for killing any living creature. Rav Yosef strongly objects to this: Perhaps this is not so, as the Rabbis disagree with Rabbi Eliezer only with regard to lice, which do not procreate. However, with regard to other abominations and crawling things that procreate, they do not disagree with him.

Anyone who does forbidden work on Shabbat even though he does not need the work itself is [nevertheless] liable for it. How is this? If he extinguishes a lamp because he needs the oil or the wick so that it not to be consumed, or so that it not be burned or that it should not crack the clay of the lamp – he is liable. For extinguishing is forbidden work and he intended to extinguish [it], even though he did not need the extinguishing itself, and he only extinguished it for the sake of the oil or for the sake of the clay or for the sake of the wick. Likewise, one who transports a thorn four ells in the public domain or extinguishes a coal so that the public is not hurt by them is liable. As even though he does not need the extinguishing itself or the transporting itself but rather [just wants] to remove the danger, he is liable. And likewise anything that is similar to this.

8. Regarding the Eight Sheratzim mentioned in the Torah {a rat, a mouse, a Tzov, a ferret, hedgehog, chameleon, lizard, snail and mole}, one who captures or bruises them is liable even though they did not bleed externally and the blood only accumulated beneath the skin. With regard to other reptiles, one is liable for beating them, only if there was external bleeding. One who captures them for a purpose is liable and one who captures them for no purpose or for no specific reason is exempt but forbidden to do so. The Rambam holds that one is liable.

And if you wish, say instead that the case where the baraita exempts from liability according to human laws the one who placed poison before the animal is referring to an item suitable for eating as well, such as afrazta, a type of herb that appears edible for animals but is actually poisonous. Therefore, this herb is halakhically equivalent to any other produce for which he is exempt from liability according to human laws, since, as Rav explained, the animal should not have eaten it.

Rav Sheshet said: I say that Rav stated this halakha while dozing and lying down, and it is not entirely precise, as it is taught in a baraita: One who places poison before another’s animal is exempt according to human laws but liable according to the laws of Heaven. From the above statement, it may be inferred that it is specifically where he put poison before the animal that he is exempt, since it is not suitable for eating. But if he put produce before it, which is suitable for eating, and the animal dies from eating it, he is also liable according to human laws. The Gemara analyzes this ruling: But why is he liable? Here also Rav’s logic can be invoked, that the animal should not have eaten it. Therefore, this baraita poses a difficulty for Rav. In order to explain Rav’s statement, the Sages said: The same is true, that even if the animal was injured by eating the produce, he would also be exempt according to human laws, and this baraita teaches us this, that even in the case of poison, which is not suitable for eating, the one who placed the poison before the animal is liable according to the laws of Heaven.

As far as the basic halakha is concerned, it was taught in a baraita that Rabbi Shimon ben Elazar says that Beit Shammai and Beit Hillel disagreed with regard to killing a louse on Shabbat: One may not kill a louse on Shabbat, this is the statement of Beit Shammai; and Beit Hillel permit doing so. In their opinion, a louse is unlike the other creatures for which one is liable for killing them on Shabbat.

10. Any animal or reptile whose bite is definitely deadly may be killed on Shabbos even if they are not chasing anyone. Other harmful animals, such as a snake or scorpion, in an area where they are not deadly, if they are chasing someone they may be exterminated and if not it is forbidden. However one is permitted to squash them in a mindless fashion, even when intending to do so, provided that one exhibits that one is not doing it intentionally.