Voles are mentioned only once in the mini-comic, "Smeltdown".
Voles are a type of rodent in the Family Cricetidae. They greatly resemble mice and are often confused with them. Voles generally have smaller ears and eyes than mice do. They reproduce rapidly and many species have short lifespans, not even exceeding a year. Voles are prey for a variety of other animals, including various birds of prey, small predators like the cat, and canids such as coyotes.
The "Water Vole" (Genus Arvicola) is mentioned specifically in the Franchise. The European Water Vole (Arvicola amphibius) occurs in most of Europe and most likely Vikings encountered these voles. Water voles are one of the few voles that live longer than a year; they can live up to 2.5 years. As their name suggests, they spend a large amount of time in the water and in watery environments such as along slow-moving water, wetlands, bogs, and moors.
The water vole is mentioned in the Franchise only as a food source for dragons, specifically Barf and Belch. In reality, humans do not have a usage for them.
In this mini-comic, Tuffnut and Ruffnut become very bored working with Hiccup's new smelting invention, the Flame-Tastic Inferno-Class Firepower-Plus. Ruffnut mentions some creatures that Barf and Belch like to eat, but upset their stomach. Tuffnut wants to feed them all those creatures, which includes water vole. Eventually, the Twins, in part, are responsible for destroying the machine.