Big spiders are not spider mites. Spider mites can be found on the bottom of the leaves and can hardly be seen without a magnifying glass. In fact, one of the ways to determine if your plant is infested with these critters is to put a piece of white paper under a damaged leaf and tap the leaf. If there are a lot of little black dots on the paper, you probably have a spider mite problem. As to whether or not the big spiders are a problem, I suspect it depends on the type of spider you have in your garden. Generally, spiders are predators and eat other insects which may cause damage to plants and really are not considered to be a problem unless they are poisoness or you hate spiders.

Smiles,
Lyn