The polyphemus moth can be distinguished from other Saturniidae by its colouring that varies from pale to dark brown and is sometimes reddish or greyish. Each of its wings has a small, scale-less “window” called an eyespot. The eyespots on its front wings are oval and encircled in yellow. The eyspots on its back wings, with yellow, dark blue and black borders, look like large eyes. Its abdomen is covered with reddish-brown hairs.
When it first hatches, the caterpillar is yellow. After four moults, it reaches a length of 8 cm or more. At this stage, the caterpillar’s body is fluorescent green and silky, with a series of small orange spots and creamy white transversal lines. The caterpillar’s head is brown.
Once it reaches maturity, the caterpillar stops eating and spends several hours weaving a cocoon. The cocoon is attached to the host plant. In southern regions, it may fall to the ground. The rigid silk cocoon, often surrounded by dead leaves, is oval-shaped and pale grey. The chrysalis spends the winter in a dormant state, protected inside the cocoon. The adult emerges the following spring.