Insect Subdomain:
insect sUBDomain Example Apocrypha (Ghlaunder): While Ghlaunder’s faithful honor the pests that carry contagion, a cult deep within the Mwangi Expanse has dedicated itself to raising giant mosquitoes. Each cultist adopts such a beast and allows it to feed on a portion of his blood every day while he seeks out and exposes himself to ever-deadlier contagions. Few survive this excruciating regimen of self-sacrifice, dictated by their unholy text The Sipping Sacrifice. Those who can sustain it hope that as their bonded companions ingest and gestate countless plagues, the vermin might metamorphose into Ghlaunder’s most beloved minions: blightspawn (Pathfinder RPG Bestiary 5 43).
Associated Domain: Animal.
Associated Deities: Achaekek*, Aldinach, Deskari*, Ghlaunder, Kitumu, Mazmezz.
Replacement Power: The domain spells provided by the Insect domain affect vermin rather than animals, treating them as if they were not immune to spells with the mindaffecting descriptor. Any such spell that allows a Will save can instead be negated by the target vermin with a successful Fortitude save at the same DC. The following granted power replaces the speak with animals power of the Animal domain. Exoskeleton (Su): As a swift action, you can grow an exoskeleton that grants you a +1 enhancement bonus to your natural armor and 1d4 temporary hit points + 1 for every 2 cleric levels you have. The natural armor bonus increases by 1 for every 5 cleric levels you have. The exoskeleton retracts after 1 round, ending its benefits. You can use this ability a number of times per day equal to 3 + your Wisdom modifier. Replacement Domain Spells: 4th—giant vermin, 5th— vermin shape IIUM, 8th—summon nature’s ally VIII (1d3 goliath stag beetles; Pathfinder RPG Bestiary 2 44).
Associated Domain: Animal.
Associated Deities: Achaekek*, Aldinach, Deskari*, Ghlaunder, Kitumu, Mazmezz.
Replacement Power: The domain spells provided by the Insect domain affect vermin rather than animals, treating them as if they were not immune to spells with the mindaffecting descriptor. Any such spell that allows a Will save can instead be negated by the target vermin with a successful Fortitude save at the same DC. The following granted power replaces the speak with animals power of the Animal domain. Exoskeleton (Su): As a swift action, you can grow an exoskeleton that grants you a +1 enhancement bonus to your natural armor and 1d4 temporary hit points + 1 for every 2 cleric levels you have. The natural armor bonus increases by 1 for every 5 cleric levels you have. The exoskeleton retracts after 1 round, ending its benefits. You can use this ability a number of times per day equal to 3 + your Wisdom modifier. Replacement Domain Spells: 4th—giant vermin, 5th— vermin shape IIUM, 8th—summon nature’s ally VIII (1d3 goliath stag beetles; Pathfinder RPG Bestiary 2 44).
Given that the subdomain affects vermin instead of animals, which companion do they get at level four?
You do not modify the animal companion domain power, and obtaining it isn't a domain spell. You get an ordinary, non-insect animal companion.
Actually, Vermin Companions can be taken by anyone who can take an unrestricted animal companion, so I think youre inthe clear.