Do I need to ground this switch?
You have a ground already.  It's called "conduit".

The locknut at the top of the box and the presence of the red and yellow wires with no black wire are dead giveaways that this installation uses metallic conduit, which is an able ground conductor all by its lonesome.

Normally, with a metal box, you'd simply make sure the switch yoke seats against the mounting ears on the box, grounding it as per 404.9(B)(1).  However, since some dimwit painted the mounting ears on the switch, you'll need to install a grounding jumper from the ground screw on the switch to a ground screw on the back of the box.


  (B) Grounding. Snap switches, including dimmer and similar control switches, shall be connected to an equipment
  grounding conductor and shall provide a means to connect
  metal faceplates to the equipment grounding conductor,
  whether or not a metal faceplate is installed. Snap switches
  shall be considered to be part of an effective ground-fault
  current path if either of the following conditions is met:
  
  (1) The switch is mounted with metal screws to a metal
  box or metal cover that is connected to an equipment
  grounding conductor or to a nonmetallic box with integral means for connecting to an equipment grounding
  conductor.
  
  2) An equipment grounding conductor or equipment
  bonding jumper is connected to an equipment grounding termination of the snap switch.