I get what you are getting at now. Well I think the fact that we have many less severe wobble morphs, when combined with spider turn into lethal or train-wreak might add to that. I mean as far as heterozygous forms go, spider seems to be the worst wobbler. based on that alone it would be reasonable to assume it would see the worst lethality of them all, then maybe, just maybe, it is so bad that it doesn't even develop fully most of the time....