Perhaps I've misunderstood, but I strongly doubt that a black-fly takes on 2 milliliters of fluid when it bites. This is equivalent to the volume of a block 1 cm x 1 cm x 2 cm in dimension. Compare this to a black-fly, and I think you'll see that this dwarfs the fly itself. No doubt the persistence of the fly and the pain and itching from the bite make one think they've consumed this much. I suspect that in fact, the volume is closer to 2 micro-liters (1/1000th the size).