Question:
Is one allowed to spray insect repellent on or toward spiders and centipedes in the house/bedroom on Shabbos? He/she will not have any Oneg Shabbos if they know the insects are running loose around the house?
Answer:
We are not allowed to kill insects on Shabbos, therefore spraying an insecticide on bugs is not permitted on Shabbos. Insect repellants very often contain insecticides in them as their active ingredients, and therefore should not be sprayed on or near the bugs, because it will kill them. It is permitted to spray it a way that will not kill them, but chase them away, such as spraying the room with it, (and keeping an open window) so they will only be repelled and not killed.
It is true, that it is very unsettling for some people when there are bugs around, but the most important facet of Shabbos is that we should not do melacha, even at the expense of oneg Shabbos. When a person keeps Shabbos, even though it is difficult, H-shem gives much more schar, and IY”H you should have much success in everything that you do in the zechus of not killing the bothersome bugs.
Best wishes
Sources:
Shmiras Shabbos Khilchoso 25-4,6, Orchos Shabbos 14-28.
