In The Hobbit, why did Gandalf say not to bring the ponies into Mirkwood?
Gandalf told the Dwarves to let the ponies loose before they entered the forest Mirkwood because Beorn requested that they do so. Beorn knew the dangers of Mirkwood: the Giant Spiders, the dark enchantments, and the fact that Sauron had taken residence in the fortress in Mirkwood, Dol Guldur. Because of those dangers, Beorn did not want to risk the lives of his ponies, whom he had a strong bond with (Beorn had a strong bond with all of the animals who lived with him, including the ponies, dogs, and also bees), so he made it quite clear that he did not want his ponies to go into the forest. Beorn also followed them to the forest to make sure that the Dwarves did as he asked, and then went home with the ponies once they were set loose.