What is leaving this white stuff on my plants?

It's a white powdery type texture on the underside of some stems:
 
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Can anyone tell me what kind of critter this is from and if it's bad?
 
Thanks!
 
Dom't think spider eggs. Most spiders have maternal instincts wrap and carry their eggs and look like littlle balls or wrap and leave them next to or in their web.  Looks like mealy bugs to me, not good some ants protect and milk them like aphids. I've heard of people wipping the affected area with alcohol wipes to kill them, and if alot of plants are affected get some lady bugs.
 
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