text: They don't, specifically.  When a mosquito feeds, it has 2 tubes, one to suck blood up to them, and another to pump fluids into you.  One of those fluids is an anti-coagulant (to keep your blood from clotting and keep it flowing freely for them), but the other fluid is a numbing agent so that you don't notice and kill them.  It's because of this numbing agent that you never feel them, you only hear them, and since they're so small and, therefore, quiet, you only hear them when they're next to your ears, making that the only time you notice them.\nSide note:  The bump and itching associated with mosquito bites doesn't show up on everyone.  It's a minor allergic reaction to the anti-coagulant and the numbing agent.  When people say "mosquitos don't bite/like me", it's not because mosquitos don't bite them, it's because they're not allergic like most of us, so without getting the bump and the itching, there's no way for them to tell they've been bitten.