Something is wrong with my holly tree

Today I noticed two holes in the trunk of my holly tree which had woodlice in them. When I poked it with a stick it seems to be a deep vertical hole (going in and up at least 6 inches). Here are some photos:



Other information that might be helpful - the tree is at least 20 years old (it was about 9 feet tall when we moved in 13 years ago); we have clay soil; no new plants have been put in near the tree; the tree is bordered on two sides by concrete maybe 4 inches from the base of the trunk; our house is rented; the tree flowered a couple of weeks ago. I'm not much of a gardener so I'm not really sure what would be helpful.

Can anyone help me figure out what is wrong with my tree? Thank you in advance!

 

Welcome to Gardeners Corner nairabell. I can't tell you what's wrong with your tree but we have a specialist that looks in from time to time, may be he can help. @HarmonyArb, any ideas please?

 

Hmm, looks suspiciously like a wood boring insect. What you have there now is a possible infection court that may leave the tree susceptible to wood decaying organisms. Monitor and keep us informed of any serious change in the tree's condition.

NB: plugging the wound will do nothing!

 

Thank you so much for your replies! I'll keep an eye on the tree. So far the leaves look okay. We've had more leaf fall than usual, but we've also had some really high winds so that could be the cause.

Harmony is there anything I can do to help the tree in the meantime?