The Mishna on today’s daf teaches:
One may overturn a bowl on top of a lamp so that fire will not take hold in the ceiling beam on Shabbat. And similarly, one may overturn a bowl on top of a child’s feces inside the house so he will not touch it and dirty himself, and on top of a scorpion so that it will not bite. Rabbi Yehuda said: An incident came before Rabban Yoḥanan ben Zakkai in his village of Arav, where a person covered a scorpion on Shabbat, and Rabban Yoḥanan said: I am concerned that he is liable to bring a sin-offering because he might have violated a Torah prohibition.
Rabban Yoḥanan did not consider the scorpion to have been potentially dangerous, otherwise he would surely have permitted it. He maintained that there was no danger and was uncertain whether or not this falls into the category of the prohibited labor of trapping (Rabbi Elazar
The Gemara discusses the ruling in the Mishna that one may cover a scorpion with a bowl on Shabbat so that it will not bite.
Rabbi Yehoshua ben Levi said: All harmful creatures are killed on Shabbat. Rav Yosef raised an objection to this from the following baraita: Five creatures may be killed even on Shabbat, and they are: The poisonous fly that is in the land of Egypt, and the hornet that is in Ninveh, and the scorpion that is in Ḥadyab, and the snake that is in Eretz Yisrael, and a mad dog in any place.
In this context, the hornet is the large hornet also found in Eretz Yisrael, the Vespa orientalis. This hornet lives in families within nests built in the ground. The hornet’s sting causes tremendous pain, even though a single sting is not fatal. There have been many instances in which people and animals have died after being stung by a swarm of hornets. The scorpion mentioned here may be the common yellow scorpion, the Ceiurus guinquestriatas, whose sting is extremely poisonous and life threatening.
The fly found in Egypt seems to refer to the gadfly of the Chrysops and Tabanus types that bite people. This bite is quite painful and causes a rash and swelling.