Dog has bald spots

Earlier today I noticed that my 7 month old lab/jack russell terrier mix has 5 or 6 bald spots.  They are about the size of a dime and located on his chest and neck.  The fur is completely gone and his skin looks red although it doesn't seem to be flaking or crusty.  He has not been itching them at all and it doesn't seem to bother him from what we can tell.  We have not changed his diet or done anything different that I can think of that would trigger an allergy.  Also, these spots they are not located under or near his collar.

Do you have any idea what this could be?  

Thank you!!

[ginger899]

Dogs can sometimes scratch at themselves when you don't see (kick with their back feet to scratch themselves) If they do it too often or too hard it can cause loss of fur. The dog I had before (a J.R.) did this, and sometimes I'd find this when I got up in the morning, and fur on the carpet.
Many times it was because he'd got bitten by an insect or something like that. It happened once when I let him swim in the river. Then the vet prescribed an insecticidal shampoo.
Once he picked up a mange mite from the fields (foxes around here carry it) and that caused loss of fur.
But usually those things cause itching and scratching, and you say you have not noticed him scratching? So I'm not sure what else could cause this. Maybe someone else will have an idea.