Locusts on the move
When I was still living in Perth (Western Australia), the newspaper reported a case of a horse race that was being abandoned and a cricket match that was cancelled for one and the same reason: invading swarms of migratory locusts, thousands upon thousands of them. What causes these insects from time to time to build up their populations to immense numbers with hundreds of millions of individuals gathering together, migrating across the land and ravaging anything green on their way of destruction? What is known is that environmental conditions are to blame.
Usually Schistocerca gregaria (the Egyptian migratory locust) and Locusta migratoria (the other important migratory species) lead rather secretive, even modest, solitary lives in the savannah belts of Africa, Asia, and Australia. A series of several very dry years taking their toll on lizards and other locust-consuming animals, followed by heavy downpours over a short period of time and the subsequent availability of lush green vegetation, however, can lead to a population explosion amongst the resident locusts. Locusts are polymorphic and with food running out, a darker colour and physically stronger variety of the usual species may then be spawned. Apart from its morphological differences the new variety displays a different behaviour and seeks the company of others: it is gregarious. At first the little wingless nymphs find each other and hop along almost as a single entity : should one insect move forward, the others next to the one that moved will do the same in order not to be left behind and gradually a massive mob of tiny black hoppers moves across the land in a single direction.
It has been estimated that locust hopper aggregations of this sort can consist of several million individuals that eat, grow and mature as they spread and devour ever more green vegetation. By the time they develop functional wings and can take to the air, covering more ground and reaching new feeding places more quickly (approx. 100km/day), dimensions of the swarms can get so big that they are detectable from satellites and can extend over several kilometres and exhibiting densities of up to 80 million/km2. Migratory routes are usually downwind towards areas of low pressure and a chance of precipitation and green pastures.
In the 14th and 17th century extensive locusts swarms even reached central Europe. Should however, the wind carry the smells of fresh grass, then the ever-hungry insects will make a u-turn and head into the wind, seeking the place of the grass smell’s origin. A huge locust swarm can consume up to 80,000 tons of greenery per day and areas vacated by the locust can easily be identified by satellites on account of their brown coloration versus the green colour of regions not visited by the locusts.
Since time and place of locust swarm formations are still largely unpredictable, precautions and warnings are difficult to issue. Perhaps rather than fighting and destroying the locusts, it might be wiser to use them, as fodder for animals (swine and poultry love them) or as food for humans. After all, they are ‘kosher’ according to the Bible and are undoubtedly more nutritious than the vegetable food they have been feasting and maturing on.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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