bug bites

Question
I have a long haired German shepherd who has K9 advantix on all year long.  He doesn't have any fleas or ticks but today he chewed a spot raw in the middle of his tail.  what could have caused it?

Answer
There could be a number of explanations.  Sometimes dogs chew on themselves out of boredom, or allergies.  If your dog spends a lot of time alone, I might suspect boredom.  You could try some Bitter Apple spray on the hair around the area (not on the raw, bare skin) to discourage him, and also provide challenging toys to keep him busy when you're not home.

https://www.premier.com/store/Products.aspx?cid=3
http://www.marinhumanesociety.org/Behavior/Handouts/KongsHomeAlone.pdf