Organisational strategy is top-down, specific, defined and visible.
Organisational stigmergy is bottom-up, loosely-coupled, always emerging and mostly invisible unless you know what to look for.
Stigmergy arises when people figure out useful things to do within an organisation and implement them without permission. Their actions often leave subtle signals for others to follow and create their own stigmergies.
Stigmergy can sometimes run counter to strategy but generally it’s a good thing and should be encouraged.