Locust - Swarming Behaviour

Swarming Behaviour

There is no consistent taxonomic distinction between locust and grasshopper species; the basis for the definition is whether a species forms swarms under intermittently suitable conditions. In English the term "locust" is used for grasshopper species that change morphologically and behaviourally on crowding, forming swarms that develop from bands of immature stages called hoppers. These changes are examples of phase polymorphism; they were first analysed and described by Sir Boris Petrovich Uvarov. He discovered them in his research on the desert locust, whose solitary and gregarious phases had previously been thought to be separate species. They also are referred to as statary and migratory morphs (though strictly speaking their swarms are nomadic rather than migratory). Charles Valentine Riley and Norman Criddle were also involved in achieving the understanding and control of locusts.

Research at Oxford University has identified that swarming behaviour is a response to overcrowding. Increased tactile stimulation of the hind legs causes an increase in levels of serotonin. This causes the locust to change colour, eat much more, and breed much more easily. The transformation of the locust to the swarming variety is induced by several contacts per minute over a four-hour period. It is estimated that the largest swarms have covered hundreds of square miles and consisted of many billions of locusts. Plagues of locusts appear in both the Bible and the Quran, including one of the biblical Plagues of Egypt, where locusts ate all the crops of Egypt.

In a paper in the 30 January 2009 edition of the AAAS magazine Science, Anstey, Rogers, et al. showed when desert locusts meet, their nervous systems release serotonin, which causes them to become mutually attracted, a prerequisite for swarming.