Nature Watch

[Richard]

The mystery is how they all appear (from different colonies) at around the same time all over the place.
There must be a trigger from one colony, which has started out for the day, when the temperature and day length, humidity etcetera is just right and other colonies milling round on the surface catch scent of them.
It is known that moths can trace scents for a number of miles overground, so why not ants?

The larger queen will be mated whilst flying but the smaller male dies soon afterwards while she drifts to the ground and burrows into the soft earth (a storm subsiding or damp conditions would be ideal to enable digging).
Eggs are laid in the colony who live underground waiting for just the right weather conditions, the following year.
Something along the lines of a wasp-nest or beehive underneath the earth.