I have just spent about a week of my spare time studying Worms and the Worm cocooning event. My original goal was to determine the lifespan of Worms for the lifespans chart in the FAQ section. I discovered how easy Worm hatching really is, and its benefits, so I explored a little more. (And, I'm now deriving lifespans for all the hatched breeds.)
Here are the basics:

Your Worm can be born on any week. That's correct. I got several worms to cocoon that were born on a variety of weeks.

The breed it hatches into has no bearing on lifespan. I created a worm by comboing 2 from a CD, born on July 1. I saved my game a month before the cocoon event. Then I hatched over and over, raising the resultant offpsring. All of them got their retirement warnings on the same week. So, clearly breed has no effect on lifespan.

However, one weird fact:

The Worm I raised that was born on May 3 has its hatched offspring live a total number of 15 weeks longer than the monster born on July 1. (I thought that being born on July 1 would give the monster almost an extra year of life compared to one born in June.) It turns out that there is some sort of lifespan formula based on the Worm's birthday. The lifespan does not "reset" after cocooning. (It's still much greater than an un-cocooned worm!)

Born: May 3, Lived 9y/5m/2wks
Born: July1, Lived 9y/1m/3wks

This 3m/3w difference is very weird, but is hard wired into each worm regardless of what it hatched into. (and its all better than an unhatched worm which has a total possible lifespan of 7y/3w.) The major difference I saw was that the mid-life warning "Most Important Stage" happened in the worms born in July before they cocooned, it happened after cocooning in the ones born in May.


Your hatched monster with a Worm sub-breed has a longer lifespan than a worm that never cocoons. Check the FAQ section, "Lifespans of All Pure-Breed Monsters" for a chart showing lifespans for these monsters.

Your Monster will Cocoon on week 4 of June, if it is "Very Well" and has no stress or fatigue My test monsters were simply rested every week of their lives, and cocooned every time. However, in experiments, simply doing a light drill (the only one their entire life!) on June 3 meant that the Worm did not cocoon. My personal recommendadtion is to rest on Week 2 & 3 of June and, just to be certain, feed 2 Mint, 2 Taffy on Week 3.

Your Worm's stats will carry over, and so will the techs -with tech transformations based on breed. Nate Railsback's recommendation of raising the stats Worms learn easily, if you are going for an opposite type monster, is great advice.

There are 7 main breeds you can get. They are: Gali, Golem, Hare, Jell, Monol, Naga, Pixie.

Main breed you get is random. So far, there doesn't seem to be a pattern to this, I just keep getting all the types. (So far, out of 28 tries I have gotten: 3 Hare, 4 Pixie, 4 Jell, 2 Naga, 7 Monol, 4 Gali, 4 Golem.) I think the rationale for the breeds you get as a result of cocooning is something like this: there are 20 mains in the game, 8 of which are made by accomplishing something in gameplay (thus not to be made too easy to get any other way) and 3 are available in the Market. So, all the rest are available through cocooning -except plant and disc. Now, when you shrine a disc, you are first told your shrining was a dud, then the guy says that you just got the soul of a monster, they are a bit special. As for plant, maybe it just seemed too weird, or they forgot about it!

The sub-breed is always Worm. this means that monsters with no Worm sub-breed (Ape, Doodle, Disc, Dragon, Ghost, Henger, Magic, Nya) will never be created by hatching. It never hatches into a Worm, either. (leaving 11 breeds, theoretically, to transform into, however, I have only seen 7 breeds emerge.

Possible Breeds:
Gali/Worm
Golem/Worm
Hare/Worm
Jell/Worm
Monol/Worm
Naga/Worm
Pixie/Worm
That's it, no other breeds are possible.

Hope this helps anyone who may be contemplating raising a Worm.
My other basic recommendations are to simply read the FAQ post on Items Values, and create your method based on that. I personally would feed Meat every month, and two Mint & 2 Taffy each week, while focusing on HD. The lifespan boost by the Meat, coupled with the elimination of rest should get you a champion fairly quickly, without having to resort to more complex methods, like DP's MR1 mehod.

well, now, this is pretty much the way i remember it. my memory may not be as bad as i fear...

Will a worm hatch if it fights in battles or goes to errantries (training)? Or does it have to be low stress/fatique it's whole life?