i hate all those pre made calcs, this one can't get screwed up..... http://www.geneticswizard.com/
spider gene can only be het to our knowledge, so its impossible to have a 100% chance for spider babies. both parents having the spider gene would give you 25% normal, 50% spider, 25% homozygous spider(which to date does not exists and hasn't been proven and that why its thought to be lethal)
the pair you listed should yield 50% killer butter spiders and 50% killer butters









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