They have white shining eyes, dragonish faces and necks, and skeletal black bodies. They have no flesh; their skin clings directly to their bones. Despite their menacing appearance, they are generally friendly animals.

Adult Thestrals range in weight from 125 to 225 pounds (56.70 – 102.06 kg). Males are larger than females. Thestrals can stand up to 45 inches (1.14 m) high at the shoulder and measure up to 7 feet (2.13 m) long.