Why rodent control usually falls on the landlord
In most cases, yes. A California landlord is generally responsible for treating a rat or mouse infestation and for sealing the gaps in the building where rodents get in.
Keeping a rental free of rodents is part of the landlord's duty to provide a livable home, and it is named directly in California's habitability law. Because rodents enter through the building's structure and often move between units, an infestation is usually the landlord's to handle — with professional pest control and by closing entry points — not something a tenant can solve alone with a few traps.
Responsibility can shift if a tenant's own severe neglect clearly caused the problem, but that is the exception, not the rule. Most apartment rodent problems trace back to the building itself. If your landlord is refusing to properly treat an infestation, it may be worth getting guidance about what the law requires.
This is general information about California tenant rights, not legal advice. Every situation is different.