(Question)
black caterpillars all over bush…killing needles …how do I save this bush?
(Answer)
It sounds like your spruce has an infestation of European gypsy moths. Below are two Toronto Master Garden resources and some other websites with information on how to manage this destructive pest.
https://www.torontomastergardeners.ca/index.php/spring-is-here-so-are-tree-pests/
https://www.torontomastergardeners.ca/index.php/askagardener/gypsy-moth-control/
https://extension.umass.edu/landscape/fact-sheets/gypsy-moth
https://msue.anr.msu.edu/news/gypsy_moth_caterpillars_damaging_spruce_trees
Hope these resources are helpful.