unfortunately he/she wont eat gnats or mites...id ditch the spider esp if its a chick...lays her eggs and you have a million little bastards making web all over your colas
Keep the spider or spray your plant for bugs. The spider is there because there is a source of food there for it. Spiders will eat most harmful species of bugs on your plant, yes the web can be a pain in the ass but bugs are worse.