The Hercules beetle is one of the largest beetles on Earth. Males can measure up to 180mm (7in) long. Females are much smaller and average 61.8mm (2.4in) long.

Males are most noticeable due to the large horns which protrude from their body. There is a thoracic horn which comes out from the thorax and a cephalic horn which emerges from the head. These resemble a large claw and are used for grabbing opponents in battle. Females lack these horns.

As an insect they have six legs.

Their abdomen is covered by the elytra which are hardened front wings. In males these change color based on the humidity in their environment. In low humidity it is a yellow or olive green and in high humidity it will change to black. The head of a male is black.

Females are dark brown across their entire body. An average male Hercules beetle will weigh 34g (1.2oz) while the females weigh 16.3g (0.6oz).