Roland's son, Mordred, takes the form of a giant spider when he needs to feed.
Mordred Deschain is one of The Dark Tower's most disturbing beings because he is both human and monstrous. He is conceived through the magical and bodily union of Roland Deschain and the Crimson King's offspring, Mia, making him a hybrid tied to both Roland's destiny and the supernatural forces opposing him.
After his birth in The Dark Tower, Mordred can shift between an apparently human infant and a huge spider-creature. In spider form, he hunts and consumes living beings, including his birth mother, Mia. The transformation is not merely cosmetic: it reflects his predatory nature and his connection to the were-spider lineage associated with the Crimson King.
Readers sometimes confuse Mordred with the Crimson King, who is also linked to spider imagery, or with Dandelo, another creature in the series who feeds on emotions rather than flesh. Mordred's defining feeding shape, however, is specifically the giant spider.