I'm trying to identify a story I likely heard on the podcast Escape Pod or something similar quite a few years ago.
In the story, smaller bug-like organisms live within the body of a larger bug-like organism. The smaller organisms all have very specific roles that they typically never deviate from, and that keeps the larger organism functioning. When the larger organism begins to die, the protagonist leaves her usual role and eventually travels to the head of the organism, where she finds that a member of her species has died in its role there and that is what is causing the issues.
I remember it was a great concept, but haven't been able to find it since.