Aquila (left) and Nikola (right) in critter form, as promised.
At some point during a yueman's teenage years, they will have their first molt. This molt comes with the ability to access their critter form. Their first shedded husk will not possess the genetic material suitable for reproduction. However, it will contain great nutritional value for a growing teen. Some yuemen also choose to feed it to the local megafauna if consuming it themselves does not appeal to them.
Subsequent yuemen molts occur once a rotation, all just prior to the Season of Sleep, when the Nightmare Gods influence is strongest over the moon and agitates the local megafauna. The husks that result from these molts possess the genetic material capable of reproduction. The husks are delivered and handed off to specific pterayukan cohorts, who take over the process of dissolving the husks into a slurry which mingles with other melted husks.