LONDON (AlertNet) - A plague of locusts sweeping across West Africa has spread to Chad and threatens to reach as far as Sudan, where it could take root before leaping continents and spreading as far as India.

Here are some key facts about locusts and the current swarm in northwest Africa.

*The desert locust is the single most destructive insect. It is native to Africa, the Middle East and western Asia. A locust measures only 4.5 cm to 6 cm (1.7-2.4 inches) long and weighs two grams but manages to eat its own weight in food every day.

* If an area is unable to support localised populations of locusts they will gather into a single mass, or swarm. This is often precipitated by favourable breeding conditions, which leads to over-crowding and scarcity of food.

* Locust swarms vary from less than one square kilometre to several hundred square kilometres. In each square kilometre there can be between 40 million and 80 million locusts. Swarms can travel 130 kilometres or more per day.

* Large locust swarms, or plagues, develop intermittently. In the last century, plagues occurred in 1926-34, 1940-48, 1949-63, 1967-69 and 1986-89.

(Source: Desert Locust Information Service, www.fao.org)