I believe the quote, made by Dante to Virgil, concerns the people in this portion of hell, who are running around, trying to escape the stings of the hornets and wasps, but who can never do anything concrete - can never make any kind of a decision. This reflects the fact that in life, they did not make a definite decision to serve God - they only served their own self-interests. The black haze mentioned by Dante in the quote refers to the swarms of stinging insects attacking these people's faces, making them bleed. I think it shows Dante's horror at their plight as he cries out to Virgil, asking what is happening to these poor people.
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