It's important to be careful about using terms that could be misconstrued or considered insensitive. "Vermin" is often used to refer to animals that are considered pests, and using the word in this context could be seen as dehumanizing or harmful.
If you're asking about animals used in composting toilets, the most common are earthworms. Earthworms help break down organic waste, turning it into valuable compost.
It's important to note that composting toilets are a specific type of toilet that uses natural processes to break down waste. They are not the same thing as regular toilets that use water and sewer systems.