The forgotten Spiders of Mirkwood

In the Silmarillion, it mentions that Ungoliant frightened even Melkor when she wanted the Silmarils(I forgot where). Ungoliant was definitely the mother of Shelob, and she was definitely the mother of the Mirkwood spiders. But in LOTR, it mentions husbands Shelob has killed. Now ponder for a moment, and consider this: where did her mates come from? Were they children of Ungoliant, or some other evil from too far back to remember? If you could enlighten me, I would be most grateful.