A red fox (vulpes vulpes) is one of the most numerous types of foxes, and is found throughout much of North America, and nearly all of Eurasia. It is one of the most well known and iconic foxes in the world.
In Empress Theresa, a red fox is the host used by the alien force HAL before he bonds with Theresa Sullivan. It first appears to Theresa while she's reading a book on her family's porch. She finds it odd, since "red foxes were never seen in broad daylight during the summer months." The fox approaches Theresa, then hunches down and studies her. Suddenly, a "softball sized white ball emerged from the fox" and went right into Theresa's stomach. Theresa darts into her house, while the fox disappears into the woods.
It is revealed later that, before Theresa was born, the fox appeared to Theresa's mother while she was raking leaves. Peter Blair comments that this meant Theresa must be "remarkable" if HAL was interested in her mother.