FAQ for
Jeepers Creepers (2001) More at IMDbPro »

It's a demonic creature with the ability to fly, extreme strength and durability, and some intelligence (including the ability to maintain and drive a car, wear a human disguise, carve weapons out of bone, and create grotesque "tapestry" out of human corpses). It uses these abilities for 23 days every 23 years in order to replace all of its body parts aside from the wings and a kind of web-like component that overlaps the creature (and particularly its head).

No explanation of the creature's origins is given, other than that it has apparently been awakening to feed for centuries (there are hundreds of corpses in the creature's lair, and in Jeepers Creepers 2, we find out that some of them are more than 200 years old). The directors have hinted that it might have originally been human at one point, a very long time ago, but it is not now.

One possibility is that the creature is a chimera of sorts, with two parts: the web/wing, and the human body parts. In the second movie, there is a part where the web/wing replaces the Creeper's head. It is possible that the web/wing is the actual "Creeper" itself, and the human body parts are simply a means of movement and survival. I hope you found out what you needed to know :)