When locust migration goes wrong
Long distance migration is an important strategy for surviving in an environment where resources (food and habitats suitable for breeding) are highly unpredictable in time and space. Locusts often undertake nocturnal, wind-assisted migratory flights at heights up to 1000 m. But migration is also risky and sometimes many locusts die in the process.
When locusts migrate long distances the direction of movement is largely determined by the upper level wind direction. The winds may take them into areas of suitable habitat where rain has or is about to fall, but swarms may get blown into areas that are totally unsuitable or too dry for breeding. When this occurs they will continue to migrate until they reach suitable habitat or until their fat reserves are depleted.
During major plagues it is not unusual to receive reports of locusts being found washed up along the beaches of southern Australia or in the guts of fish after swarms were blown out to sea. Offshore migration was considered to be a major factor leading to the collapse of the 1973-74 Australian plague locust outbreak.
A spectacular example of how locust migration can go wrong was discovered on Lake Frome, South Australia, in January 2001 by scientists from the CSIRO Earth Observation Centre. The flat, bright white surface of this normally dry salt lake was being used to test imagery from a NASA satellite. When satellite pictures of the lake were analysed by CSIRO, several new dark lines were detected near a group of islands. Ground crews investigating these new features found strand lines formed by dead locusts.
These dead locusts were almost certainly part of the large infestation that occurred in the region in autumn 2000. At that time the lake contained water after record summer rains. It is possible that the moon reflecting off the water may have disoriented migrating locusts. The action of the wind would have concentrated the drowned locusts along the shoreline. When the water evaporated the dead locusts were left behind forming strand lines of bodies so large that they were detectable from space.