You're either brave or desperate to accept this job. We used to smoke-flash bloodflies with full crews, but the infestations are bad now and the Duke cancelled the funding. So we get rid of nests by hand.
Here's what you need to know to stay alive.
1) If you need to slip past a bloodfly swarm or nest, keep your distance and move slowly, or they'll attack.
2) When the bloodflies are calm, you're fine. If they take flight and start glowing, it's trouble.
3) If you get swarmed, you gotta run away or fight. Smash the bloodflies or burn them. Same for the nests.
4) A bloodfly swarm'll keep coming back until you destroy the nest for that swarm.
That's reallys all you need to know. You'll do fine.
Oh, yeah, another thing. If you find any blood amber in a nest, just keep it as a bonus. But make sure the Grand Guard doesn't see it, or they'll ask for some "urban sanitation tax" or whatever. Good luck.