If the ant clings to something much heavier, like a school bag, then there will in fact be much more air resistance. In addition, the force from gravity will be much larger, and able to overcome this air resistance. Thus, the terminal velocity will be much greater.
You can predict this effect qualitatively simply because the force of gravity scales with volume (since this is proportional to the total mass), while the force of air resistance scales with surface area. So, if you double the object's dimensions, the force of gravity goes up as length cubed, and the force of wind resistance goes up as length squared.
These effects are important: heavy sky divers fall appreciably faster than light ones, and so use larger canopies.
So yes, the ant will probably be squashed, unless your school bag has a parachute inside.
(published on 05/18/13)