Ants don’t kill trees but they can be attracted to diseased/dying trees.  Needles fall off for a variety of reasons including diseases. In general healthy trees drop needles/brown needles either because it's time to grow new ones or they are stressed by lack of water or  nutrients. The lower and inner needles can also drop because they are shaded and can’t photosynthesize normally. 
My best guess from the picture is that this is normal needle regeneration. However I can’t rule out rhizophera needle cast which commonly infects Colorado blue spruce which I also see in the picture. It sometimes also infects other spruce trees such as Black Hills/white spruce.  The websites give additional information on what to look for.
See: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/choosing-landscape-evergreens/ 

For spruce tree diseases see:

https://apps.extension.umn.edu/garden/diagnose/plant/evergreen/spruce/needlesdiscolored.html