Nice overall...
...and I'm really sorry to say that, but I do not exactly see how this is comical? When you announce something like that and explicitly point to its short duration, I as a viewer - and probably others as well - expect some sort of comic relief at the end. This, however, looks more like the beginning of a series - and, indeed, I would encourage you to consider finishing the story about the rogue flea, which despite having no wings, is well drawn and animated; actually, the mutated fly reminded me of Gary Larson's drawings. Enjoyable short, keep going at it.