Finish the body using the photo as guidance. Add another triangle shape at the rear. The two rear spars are half-thickness to allow the tail hook to fit between. Form the tail hook from a large paperclip. Scuff the tail hook and superglue to the rear triangle. Reinforce tail hook with tissue paper.
After flying and crashing my ornithopter for several days, it broke right at the weak point between the triangles. So I added a third spar high enough to avoid the rubber band motion. I recommend you add one as well, as pictured.