Ants - yes, those insects that we all must suffer from at times - have a reputation of being shrewd observers, and even predictors, of the weather. As rain approaches, it is said, they can be seen running to and fro, carrying their eggs to a more protected spot. One of the earliest persons to note this precautionary ritual was the Roman poet Virgil, whose comments on the subject were translated into English by John Dryden in the 17th century:
For 'ere the rising winds begin to roar,
The careful ant her secret cell forsakes.
Now, the ants' behaviour in this context may well be prompted by subtle changes in humidity that are undetectable to you and me, and this has given rise to the superstition, common in many cultures, that stepping on ants will bring the rain; but on the other hand, some would argue that if the ants are there to be stepped upon in the first place, it may well be that the rain is on the way in any case.
It is often said, however, that it is not to what the ants are doing, but to how they do it, that we ought to look for weather clues. We are told, for example, that when they expect bad weather, they travel in straight, regimented lines, whereas if good weather is on the way ants going about their normal business spread out and cover wide areas.
Moreover, they allegedly run faster in warm weather than when it is cool, to the extent that an approximation to the air temperature may be obtained by timing the speed of movement of these busy insects.
It may be in this thermometric skill that we can find the answer to periodic swarms of these particular insects. Continuation of the species depends on the successful mating "on the wing" of the winged males and queens in summer, an exercise which, as you may well know from personal experience, is most effectively accomplished in dry and calm conditions.
The eager potential procreators are carefully pampered in their nests by the wingless workers, often for several weeks, until conditions are exactly right.
Meanwhile, the workers monitor the temperature and humidity outside, waiting for the perfect mating weather to arrive. When a period of stable anticyclonic weather is at hand, the worker ants release a chemical into the air that stimulates the males and queens to emerge simultaneously from hundreds of nests over many square miles. The result is a swarm, common in summertime, during which many an antly nuptial is consummated.