Sadly I've been looking into the same thing though I'm a senior now and I've only found one and that's Ohio State University. Kent State I believe offers a minor not a major and both of these are in entomology... I can infer that in order to branch off into arachnology you first have to take entomology.
There are actually several that offer degrees in what you are seeking. Arachnology can be studied at a university in TX (was it A&M maybe?) while if you're looking for entomology there are several more options, including nebraska, missouri, perhaps CSU, and several others. If you do some google searching, you'll find a decent listing. I'm currently getting my masters in entomology through the university of nebraska.