I knew someone was gonna correct me...
Spiders aren't known for spitting. It's not a defining characteristic that has been popularized by popular media throughout time, and therefore is not a commonly understood trait. The same way duck billed platypuses aren't known for having one of the most painful venoms in the world that they inject through a toe spike. It may be true, but it's not what they're most known for. (They're most known for defeating the evil Dr. Doofenshmirtz in Danville of the Tri-State area, of course.)