its been raining the past couple of days.
they say that when you kill a spider that it rains right. im thinking spiders have a sense about when the rain is coming, and head inside before hand, getting them killed.
like with how birds know when a storm is coming.
spiders are small, they can most likely feel the change in weather better than we can. as 1 degree isnt much to us, it'd be a lot to them.