The Harpies of ancient Greek mythology were small, half-human, quite disgusting birdlike creatures, with long sharp claws and faces pale from the pangs of ever-present hunger.
They came in flocks or swarms, evil harbingers of stench and foul decay, contaminating everything they came in contact with. And they were greedy beings, scavenging every scrap of food from in front of those whom the gods had sent them to torment.
It has been suggested that the Greeks may have based their notion of the harpies on the desert locust. Although only a few inches in length, and in appearance not dissimilar to a grasshopper, a migrating swarm of hundreds of millions of these hungry insects consumes everything edible in its path, and wreaks havoc on a massive scale. The Irish Times reported on Saturday that such a plague had recently appeared in southern Australia.
For most of the time a typical member of the family Schistocerca gregaria lives a quiet and unobtrusive life. Local farmers may not even be aware of him - or her. Every now and then, however, biological and climatic factors conspire to cause a swarm.
A small swarm may contain a mere 10 million locusts; a very large one may occupy an area the size of Co Dublin, and contain 100 billion insects with a weight approaching 20,000 tonnes.
When you consider that a swarming locust likes to eat its own body-weight in food every day, the potential for destruction becomes obvious.
The life-cycle of the locust lasts about two months, beginning when the eggs are laid a few inches below the ground. Prolific hatching occurs, however, only if the soil has been moistened by heavy rain in the recent past, so a plague develops following the fortuitous occurrence of plentiful rainfall in the different hatching grounds of a few successive generations.
Given the necessary meteorological conditions, and some biological signals still imperfectly understood, the insects multiply at unbelievable rates, and the current south Australian plague is a consequence of unusually abundant rains over the normally parched outback areas.
The life of the locust is a constant search for food. When they have exhausted the supply in a particular area, the insects take to the air to be carried by the wind to a new location. As a rule they fly by day, travelling several hundred kilometres, and then roost and feed at night.
Accurate wind forecasts for a day or two ahead allow the future position of a swarm to be anticipated, and the necessary resources can then be deployed in advance to attempt its eradication.