Power washing the shelves from outside and saw a web.  Looks like a brown widow.  Yep that's a widow.   The bite of a brown widow is "The two major symptoms of a brown widow bite were that the bite hurt when it was inflicted and it left a red mark."  Interestingly the brown widow is out competing the black widow which typically gives a much nastier bite.  Still they can't live in the greenhouse.
 

So many little critters we have to watch out for.  Glad you found it before it had a chance to do any damage.

We tend to see a few black widows every year around our yard.  I've never seen a brown one.  Glad you got rid of this one!

We have both in SoCal.  Found a couple of brown widows in my mailbox (shudder) over the years, I always bring a flashlight now when I check it after dark.

From my reading the browns are pushing out the blacks.  From a people point of view the brown is better since they are much less aggressive and bite is pretty harmless unless you are sensitive to the venom.

Uh, spiders just freak me out. YES, keep the greenhouse!

One good thing about the cold is it keeps all the nasty critters away! I don't have to worry about any of that. Growing up as a child I use to pick up snakes and spiders to scare my siblings :)