system
Given the following post, respond as if you're commenting on Reddit:
human
[Dune] Are the sandworms composite beings by nature?

From what I know,  Leto II's transformation happened after he merged with many sandtrouts then underwent a slow change for thousands of years. I might have missed a thing or two here.
gpt
No, Leto's transformation was very different from the normal lifecycle of a Sand Trout.  Well, more that it was a unique life cycle resulting from some odd circumstances.

Under normal conditions one of two things happen with Sand Trout.  Left alone, they can survive long enough to grow into a small sandworm that, over time (thousands of years), grows into a full size sandworm.  The second thing that can happen is they can find water, at which point they surround the water and attach to one another forming a living cistern that surrounds the water completely.  Those trout are eventually killed in a later ensuing spice blow when the trout, water and spice all interact.

Leto's circumstances were a unique combination of the two.  Basically the trout formed a cistern around his body's water as usual, but he was so pumped full of spice that instead of going through the spice blow process they merged with him turning him into a human/sandtrout hybrid.  Once that happened he underwent the normal lifecycle growing into a full sandworm (hybrid).