I would argue that the answer is something simpler and more basic: Mosquitoes are the aggressor. You merely defend yourself. Ants, cows, cats, dogs -- these creatures do not attack you. They do not attempt to sup on your body. Or poison you. Or possibly give you malaria. As you say, it is not murder. But neither would it be murder for you to kill a human being who attacked you to try to feed off of you.

Hm. I might have to go with youtube on this one. In the context of your blog post, yes, fair use. It's a small clip out of an editorial. In the context of *youtube* -- which is the context you were uploading the clip to, after all -- it's just a 90 second clip from their movie. No editorial, it's the entire thing. Someone browsing youtube who finds it will have no idea that there was a blog connected to it. For Fair Use protection, you'd have to make a video of someone reading your blog post, with the movie at the appropriate time.