The above quote is the only part of JodanOrNoDan's post I have a problem with. And that is because it can be interpreted in several ways:
1. If two spider ball pythons are bred together, one or both adults is certain to die before the eggs are laid. This is false. Mortality is no worse than when a spider ball python is mated to a normal. And, of course, all ball pythons die sooner or later.
2. If two spider ball pythons are bred together, all of the eggs will die before hatching. This is false.
3. Here is what is true, to the best of my knowledge and experience with lethal genes in other species. If two spider ball pythons are bred together, 1/4 of the eggs are expected to contain embryos with two spider genes, 2/4 of the eggs are expected to contain embryos with a spider gene paired with a normal gene, and 1/4 of the eggs are expected to contain embryos with two normal genes. Embryos having a spider gene paired with a normal gene hatch out as spider ball pythons. Embryos having two normal genes hatch out as normal (non-spider) ball pythons. These spider and normal ball pythons have the same survival chances as spider and normal ball pythons from a spider ball python x normal mating. Embryos having two spider genes die before hatching.
If I wanted to mate two spider ball pythons, I would do it. Your mileage may vary.
Yes, all this is correct. I was too lazy to type it though. I maybe should have clarified. Having spider on both sides of the ladder is lethal. I don't do the cross because I do not want my females producing non-viable embryos if it can be prevented.