On one hand, the spider is a symbol of poisonous and sinful desires..... and an emblem of skillful and creative attitudes, on the other.
A dream of spiders could be warning to not get 'caught up' in things.
It could also be symbolic of a fear of getting 'caught in a web' ...or 'trapped' in a situation.

Arm(s) - an extension of yourself, a means of expression and protection. To see your arms as the emphasis in your dream, indicates your nurturing side, and your ability to reach out and care for people. Alternatively, it may represent the struggles and challenges in your life.

Right arm - signifies your outgoing nature and is associated with masculine energy.

Skin - represents protection or shielding of your inner self. It serves as a physical boundary and how close you let others get to you. Your contact with the world, what tactics you use to deal with others, strength or vulnerability in feeling the impact of other people: their remarks and actions.
Something under your skin would represent something, or someone, that is bothering you.

Strangers - If the person reminds you of someone you know, think about your relationship with him or her, and the issues that the dream has brought up, or how you relate to the person that is being represented. If these people are totally unrecognizable (they don't remind you of anyone you know)... they would represent different, and unknown, aspects of yourself. They are extensions and projections of your own subconscious, and personality. Alternately, a stranger may represent an unknown fear, or danger, you feel in your waking life.
That he asks you, "What are you going to do about..." , suggests that you are facing a situation that you need to act upon. Something, or someone, you may have forgotten about, or have been reluctant to face or deal with.
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Are you feeling 'caught up' in a situation?
Is there someone, or something, that is really bothering you....or gotten under your skin?
Are you feeling trapped, or ensnared, by someone?


Hope this helps, good luck!!