This is a very different comic than I was originally going to post.  The saliva mosquitoes inject when they suck out blood is what makes people itchy.  I’m fairly certain that they withdraw the saliva when they finish sucking blood, meaning that the itch would be minimal if present at all, but for the most part they’re stopped partway through.  However, I couldn’t find a credible source to back that information, so it may be “bull-ogna”!