When I Was a Prevented Predator

A body divided into two distinct parts,
The collum, right behind the head, it sits;
The head houses the eyes, antennae and mouthparts,
The first part is the first body ring in a body with lots of rings,
The second part, the trunk, consists of several body rings;
I spotted her wriggling around with her four body rings,
The male had deposited a sperm packet on the ground,
The female millipede just picked it up and said: what a find!
I moved closer, she veiled a chemical that made me unsound!