Ants

The stonemason working on repairing our garden walls called me over to see this. As he was clearing away the old mortar / cement, one of the stones fell off and exposed this ants' nest.

He's never seen such a size of a nest in a wall. They have clearly been there for a while. What was fascinating was watching the ants. Many fell to the soil and scurried around. Those that stayed on the wall immediately set to to protect the eggs/larvae (see in the centre). Within 3 or 4 minutes they had all been moved further into the wall to protect them.