Member of the Month: May 2009, Oct 2010, Sept 2017
Spiders? Leave them alone, lol, they eat insects not plants.
If you meant to type "spider mites," that's different and they would need to be dealt with. I've found that a good, thorough spray with a shower head or the sprayer on a kitchen sink will remove them from plants. Unfortunately, it may leave some eggs in the soil (if the plants are rooted and growing in soil that you cannot easily/simply remove them from).
If that's the case... What I do is remove them from their containers, blast them from every direction with water as mentioned, shake most of the water off, and then thoroughly drench them and any remaining soil with a product such as Safer's Soap or the like -and then repot them and proceed as per normal.
You can add a thin layer of food grade diatomaceous earth (after the top layer of media dries), which will kill and soft-bodied critters that crawl over it. It's nontoxic. However, it doesn't work when wet.