How is that possible?

I have read that spider physiology has some aspects that are radically different from insects but I don't know what in particular might account for an ability to remain active in very cold conditions.

Like overwintering insects, spiders might take awhile to build up cold resistance, so popping one directly into the freezer to test the hypothesis might not be a valid test.

I usually see them dead in their webs after the first freeze but it has been very un-seasonably warm here. I am wondering what a spider could expect to catch in the web at sub freezing Temps.

There's nothing that would fly when it's that cold but the spiders could get webs ready for the next warm spell.

I remember hearing that some NASA biologists were trying to determine what life forms might be able to withstand the low oxygen, low temperature Martian climate when one asserted that spiders would probably survive there given a food source. I never thought much more about it till I saw the sub-zero web spinning.