Glomachs have changed since I've been developing Balphrahn. Initially, they were a type of weasel, but with shaggier fur. One day I was wondering through the taxidermy at the Field Museum. I found the South African Springhare and knew that was what I had been looking for.
In terms of North American mammals, they're a cross between squirrels and rabbits. However, glomachs aren't ordinary rodents. They have an adaptation that allows them to be invisible to magic senses. Without spoiling anything, I can tell you that will be handy for one of the characters.
Glomachs are part of the fairy family, and they help monitor the magical border between Slan and Annwn. They investigate border breaches, and if they sense the person means no harm, they will follow and watch. If the person does mean harm, they scatter and leave them to the nearest water dragon.
While glomachs do stray across the border into Slan, they are rarely seen. They are shy and hide well.