First of all I have had small spiders in my auratus tank and they have been just fine, if anything lunch. I would make sure the spider is not poisonous by looking it up. As for your frogs being able to use it's venom if I remember right it is a difficult process to mimic to make them poisonous, I believe the termites have to eat a certain plant and then the frog eat the termite or something along those lines. Hope this helped
Curtis
Curtis