Ant damage?

[Tony Croft aka hamadryad]

Its a sequence of invaders, the ants could simply be farming aphids for honeydew high in the canopy or nesting/repairing the nest after mr yaffles been after a few boring grubs.

 

the value of decay and deadwood, so much life in what is to most rubbish or just plain ugly.

[Arbgirl]

Goat moth caterpillars do burrow together

 

European goat moth, Cossus cossus (Lepidoptera: Cossidae)

 

The frass also makes me think you are correct about Goat Moth too

 

They are known on old Willow and are quite a rare moth