Males have been seen clustering together at high ground while they wait for females to come and mate with them. This behavior is called "hilltopping". Once they have mated, adult females work tirelessly, living only about 3 to 4 weeks, boring as many holes and laying as many eggs as they can before dying. In that short life span, she can lay over 300 eggs, each in their own hole.
Because this species prefers conifer trees like pine, it is not uncommon to see adults indoors as they emerge from wood that was harvested and used to build things while they were still inside developing. The whole life of a Banded Horntail, from larva to adult, can last 3 years.