Insect and Spider Identification: CLOSED: ants, 4 by Weerobin

Weerobin wrote:
This is a repeat of a post I placed on trees forum yesterday.
It was suggested I re-post it here to get you guys' opinion.

I was pruning a Japanese apricot (prunus mume) yesterday.
One limb had a deep cleft in it where ants appeared to be entering & leaving frequently.
I cut the limb off as close to the trunk (pic #1) as I could.
But it appears there is a central rotted area where ants are still living (#2-4).
I realize prunus mume is prone to all sorts of pestilence,
but it's winter bloom is truly remarkable - pic #5 was taken on New Years Day!
If the tree is the only thing at risk, I'll take my chances.
But if my house is at risk (it's adjacent to the attached deck), I'll take the tree out.
The tree otherwise looks healthy - it grows like crazy, which is why it needs frequent pruning.

The advice on trees forum was to see if the type of ant could be identified,
to determine if it's a type which could threaten my house,
rather than just living off the dead wood in my apricot.
Any ideas?
TIA.