Bloodfly Infestation is a written note found in Dishonored 2.
I'd like to offer my apologies for being such a grumpy captain.
Second, my apologies to [Lord Corvo, who/Lady Emily, who/whoever] broke the bloodfly tank, allowing them to flutter down to the engine room, bringing joy to this sad boat of mine, with the gentle humming of their soft wings. I deeply regret calling you a clumsy sack of guano.
But now that we've all had time to enjoy their charming company, can someone please exterminate every last bloodfly on my ship?
It can be found aboard the Dreadful Wale, pinned to the broken glass case in Sokolov's cabin during the mission The Royal Conservatory. If the protagonist broke the glass case, his or her name will be mentioned as the one responsible for it.