This person spared a spider’s life but then it multiplied
Spiders are great at pest control, so it is beneficial for humans to keep them around. For example, they keep the mosquito population in check. They also kill other insect species that can harm crops.
So, it is better not to kill them if you ever find one scurrying around your house, which is what this homeowner did. Little did they know that the single critter would reproduce and multiply so quickly.