The Spider is a main antagonist from the film The Secret of NIMH. It is a large spider that almost sneaks up and attacks Mrs. Brisby.
The Spider is only seen in the movie where it comes down from a web and proceeds to follow Mrs. Brisby in the owl's tree trunk. Mrs. Brisby is unaware that the Spider is behind her and is about to attack her.
Just when the Spider is about to attack Mrs. Brisby, the owl steps on it and kills it. If it wasn't for the owl, the spider would have easily killed Mrs. Brisby on the spot.