Red wolves are a species of wolves that appear in the animated series.
Only one member of the species is ever seen in the show itself, and serves as the primary antagonsit of the season 2 episode "Chapter 9: The Deerfox". It is however confirmed by "Hilda's World: A guide to Trolberg, the wilderness, and beyond" that there are more red wolves, since the book warns travelers going into the wilderness to look out for the animals. This is further proven in "Chapter 2: The Fairy Mound", when Astrid mentions "Red Wolves".
Red wolves look like regular wolves but with red fur. They are carnivorous in nature. Since the red wolf from "Chapter 9: The Deerfox" was alone, this could indicate red wolves are solitary creatures whereas regular wolves live in packs.