Yeah I'm new to this also.sorry.
But one on the left is the most/shell of the spider on the right(they molt like crustations, leaving behind there old skin). As far as the spider I would think benefit of eating those critters that might have negative effect.however "spider mites" might come from spiders hense the name (I know spider mites are a nuseance) that being said ladybugs,spiders, etc for me i leave and are benifical but that's just me