A few desert locusts, swarms of which invaded Egypt and other North African countries, have been spotted in Malta and Gozo over the past days.
Several readers of The Times have reported seeing individual locusts or pairs in various parts of Malta and Gozo. A locust was seen at St Andrews on Thursday and others were seen yesterday in St Christopher Street, Valletta.
Locusts, that devour crops when they swarm, are harmless locally.
Locusts are part of a large group of insects commonly called grasshoppers which have big hind legs for jumping. They differ from grasshoppers as they are able to change their behaviour and habits and can migrate over large distances.
The desert locust is one of about a dozen species of short-horned grasshoppers that are known to change their behaviour and form swarms of adults or bands of wingless nymphs. The swarms that form can be dense and highly mobile.
During quiet periods desert locusts are usually restricted to the semi-arid and arid deserts of Africa, the Near East and South-West Asia that receive less than 200mm of rain annually. This is an area of about 16 million square kilometres, covering about 30 countries.
During plagues, desert locusts may spread over an enormous area of some 29 million square kilometres, extending over or into parts of 60 countries. This is more than 20 per cent of the total land surface of the world. During plagues, the desert locust has the potential to damage the livelihood of a tenth of the world's population.
Plagues develop intermittently and during this century, desert locust plagues occurred in 1926-1934, 1940-1948, 1949-1963, 1967-1969 and 1986-1989.
A desert locust lives from three to five months although this is extremely variable and depends mostly on weather and ecological conditions.
The lifecycle comprises three stages: egg, hopper and adult. Eggs hatch in about two weeks, hoppers develop in five to six stages over a period of about 30-40 days and adults mature in about three weeks to nine months but more frequently from two to four months.
Female desert locusts lay eggs in an egg pod primarily in sandy soils at a depth of 10-15 centimetres below the surface. A solitary female lays about 95-158 eggs. Up to 1,000 egg pods have been found in one square metre.
Desert locusts usually fly with the wind at a speed of about 16-19 km/h depending on the wind. Swarms can travel 5-130 km or more in a day.
Locusts can stay in the air for long periods of time. For example, locusts regularly cross the Red Sea, a distance of 300 km. In the past there have been some spectacular and very long distance swarm migrations, for example from North-West Africa to the British Isles in 1954 and from West Africa to the Caribbean, a distance of 5,000 km in about 10 days in 1988. Solitary desert locust adults usually fly at night whereas gregarious adults (swarms) fly during the day.
Swarms can vary from less than one square kilometre to several hundred square kilometres. There can be at least 40 million and sometimes as many as 80 million locust adults in each square kilometre of swarm.
An adult desert locust can consume roughly its own weight in fresh food per day, that is about two grams every day. A very small part of an average swarm eats the same amount of food in one day as about 10 elephants or 25 camels or 2,500 people.
Locusts do not attack people or animals. There is no evidence that suggests that locusts carry diseases that could harm humans. People in several countries eat them. They catch them with large nets or collect them. They are then stir-fried, roasted or boiled and eaten immediately or dried and eaten later.