Answer: The most likely identity of your "mystery critters" is a new hatch of stink bugs or leaf footed plant bugs. These tend to cluster at first and when young look a bit spider-like. I can't think of a beneficial insect that would fit the description.
If they persist and grow to look more like stink bugs (which are sheild-shaped), a control spray would be in order. Products containing rotenone and pyrethrin are an organic option that are somewhat persistent and therefore should be used as a last resort.
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