As the name suggests it has the appearance of a green caterpillar.
As of chapter 169, his Charyeok seems to have matured into a butterfly, the new power gives McDonald wings that grow out of his back and gives him the ability to fly.
Regeneration: It gives him the ability to regenerate by sewing back on severed body parts.
Flight: after maturing into a butterfly it can grow a pair of wings on the back of it's user granting him the abilitiy to fly freely. The flight seems to be extremely fast judging by how McDonald with these wings out sped Axley's, though it should be noted that Axley lost one wing in his fight against Q.