Superior entry in the Universal series of Sherlock Holmes B-pictures made during WWII. The title sounds like it features one of the studio's legendary monsters, but the spider woman actually just kills her helpless victims with poisonous arachnids. After relieving them of their life insurance, naturally.
So send for Holmes and Dr. Watson. Basil Rathbone hunts down the odious gang of crooks and Nigel Bruce raises some laughs. But they are (arguably) upstaged by Gale Sondergaard who is the best villain of this whole cycle. She even starred in a 'spider woman' sequel, though- disappointingly- in a different role.
The screenplay is crammed with references to multiple Arthur Conan Doyle's stories, which is gratifying for the fans. Most obviously, The Speckled Band, though with spiders rather than snakes. Roy William Neill gets it all done in under an hour. There are no lulls and a sudden plot twist is along every few minutes.
And there's a suspenseful climax at the fairground, with the great detective tied to a target in the shooting gallery. A baby would see through Holmes' disguises, even if they are beyond Watson, who having been fooled once too often tries to yank the beard off an eccentric entomologist. It's the Universal series at about its peak.