Molting.

[Falconerguy]

I have heard a million and one horror stories where the mantis dies, or almost dies during the molt. With proper feeding and humidity and temperature, how common is this, actually? People make it out like it happens every one out of three times!

 

[wuwu]

It's not common if they're kept in the correct conditions.

 

[Falconerguy]

That makes me feel better.

 

[Rick]

It is fairly common and everybody has mismolts from time to time regardless of how good your conditions are. It is a fact of this hobby.

 

[ShieldMantid1997]

Mismolts are more common with certain species and rarer with others, but a fact that is hard to accept is no matter what you do, you may still have a mantis die or be crippled.

 

[ismart]

All you can do is pray to the great mantis god, and hope for the best. But in all reality it happens to all of us from time to time.

 

[Ranitomeya]

Mismolts are fairly common in the hobby regardless of conditions you keep mantids in. I can't help but wonder if our actions might be increasing the number of mismolts in the hobby.
Mismolted mantids in the wild would most definitely perish and fail to pass on their genes--there's a possibility that by saving mismolts and allowing them to reproduce, we may be allowing some heritable cause of mismolts to spread and exist.