Or the infestation of beetles.

I knew someone who had a condo which had rats in the attics and
ceiling.

They were poisoned, but most died in the walls or attic and their
corpses couldn't easily be retrieved, so after the stench of
decomposing wore off, a particular carrion eating beetle (don't
remember the name) came along and flourished until it ran out of dead
rat to eat and eventually died.

The whole ordeal went on for months.