A TYPICAL member of the desert locust family, Schistocerca gregaria, lives a quiet and unobtrusive life, perhaps in Mali on the western edge of the Sahara, or along the Red Sea coast of the Sudan. 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, on the other hand, may occupy an area the size of the Iveragh peninsula in Co Kerry, 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 per day, the potential for destruction becomes obvious. The author of the Book of Exodus describes it well:
"The locusts came up over the whole land of Egypt. And they covered the whole face of the earth, wasting all things. And the grass of the earth was devoured, and whatsoever fruits were on the trees; and there remained not any thing that was green on the trees, or in the herbs of the earth, in all of Egypt."
The life cycle of the desert 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 these favourable conditions, and some biological signals still imperfectly understood, the insects multiply at unbelievable rates.
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 forecast for a day or two ahead, therefore, allow the future position of a swarm to be anticipated with considerable accuracy, and resources can be deployed in advance to attempt its eradication.
More recently, weather satellites have been used to take preventative action. When rain sprinkles a normally arid area of desert, green patches of vegetation suddenly appear. These provide enough food for the first batch of insects that may ultimately form a swarm.
Weather satellites can identify these mats of unaccustomed green, and appropriate responses can be made before the problem, quite literally, takes off.