For people who have bred Spider x Spider, what is your rate of failure?

I remember hearing that Hom Spiders dont exist and that they fail to develop as embryos. If thats the case then you would get either slugs or rotten eggs. So I was wondering if anyone had noted it. Overall levels should balance out to ~25% failure rating.

I don't think there are many people who are doing this any longer, since it was proven that you don't get super-spiders.