Spider is a dominant morph, so if the animals you would be breeding are not spiders, then there is no chance of you ending up with spider babies, since neither of the parents have the spider gene. I believe you are trying to think of the spider gene, which is a dominant gene, as if it were a recessive gene like the axanthic gene. Since the spider gene is dominant, any animal who has the gene will show the trait.

If you breed two 100% het for axanthics together, you will get 1/4 axanthics, 1/2 50% possible het for axanthic (which will look normal), and 1/4 normal.

Hope this helps, and I hope I answered correctly. I am sure someone else will chime in with a more detailed answer.