How do you know if the itchy bites all over your forearm are from a spider?

I don't think it could be from a spider bite. I think maybe you are allergic to something. You should think about what kind of products might make your skin have an allergic reaction to it. It could be you used a towel that had a substance on it, like those laundry fresh sheets that you use when you put the towels in the dryer. You have to always take into consideration how sensitive skin is