I have a dog named Simba he is almost 6 years old. He is up to date on all his shots including rabies. cont.?

He takes his monthly medication for heart worm and fleas. Now he has developed an itch on his genital area. He scratches like crazy. I noticed some black spots there, I look to see if it was little animals or something and it doesn't seem like it. Does any one has any suggestions on what this could be. Or do I have to rush him to the Vet. I just need to know what it could be. We live in Florida but he is an air conditioned dog. He only goes outside to do his business and comes right back in. I appreciate any help at all. Thank you so very much. love Bori.