Today we rise - II

I barely ever see ants in our garden. Yet last weekend for some mysterious reason a large nest of several hundreds, if not thousands, erupted like a volcano. I can distinguish three types of ants: wingless workers, winged workers and a few winged queens. Every few seconds a few of the winged ones flew of, perhaps to start a new nest.

I wonder what triggered these ants on this day particularly.

Update: I just learned that what I witnessed is probably the "bride flight", where on a pressing summer day the winged queen along with many men with exit the nest in waves to start a new colony somewhere else. Upon landing, the queen will eat her own wings to provide initial energy needed to lay new eggs.