nellie stevens holly
20 year old Nellie Stevens holly tree has square holes eaten into bark around circumference of trunk has several identical rows - ten feet off ground and 15 feet off ground with sap leaking from these areas.
Certified GKH Gardening Expert
I suspect that you are looking at either carpenter bee damage or borer damage. A common borer that attacks holly is the Redheaded Ash Borer. These articles will help you determine which it might be: http://www.ento.okstate.edu/ddd/insects/redheadedashborer.htm