SEPTEMBER
2009

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

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09-10-09

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Where Have All the Locusts Gone?

Once upon a time, insects called locusts wreaked havoc upon vegetation growing in what is known as the Great Plains region of North America. Locusts are the type of insect that most people call grasshoppers. But these grasshoppers are not your average run-of-the-mill hoppers. No, these grasshoppers are what scientists call migratory locusts.

To many people in the United States, the mention of the word locust brings to mind insects that fly around in treetops and produce a humming sound. These insects are properly called cicadas. Cicadas and grasshoppers are totally different insects, but a historical twist of fate resulted in the incorrect use of the name locust.

You see when early European settlers, who as it turns out really didn't know much about insects, landed on the shores of the New World they encountered great masses of cicadas. The settlers knew something about gigantic swarms of a type of grasshopper called a locust in the old world, so the insects were dubbed with that name. Of course, the first naturalists who visited the new world quickly recognized that those locusts weren't locusts; they were cicadas. Nonetheless, the incorrect name has persisted in many quarters to this day.

When swarms of migratory locusts land, they devour crops and other vegetation. In the United States, it was reported that at times the chewing locusts even ate clothes off the line. Railroad tracks sometimes became so slick from crushed bodies of locusts that trains couldn't move because of lack of traction. While periodic swarms of migratory locusts had no doubt moved across the western plains for eons, their devastation became a major problem only when early settlers began to grow crops.

North American settlers of "The Little House on the Prairie" ilk weren't the first people to suffer from the ravages of migratory locusts. Several thousand years ago, these notorious insects rained destruction during biblical times. One of the 10 plagues visited upon Egypt preceding the Exodus of the Israelites consisted of migratory locusts that "covered the surface of the whole land, so that the land was dark; they ate up the vegetation of the land, and all the fruit on the trees or shrub in the fields all through the land of Egypt." To this day, plagues of locusts still sometimes move across northern Africa, leaving destruction in their wake.

It is difficult to say anything good about migratory locusts. The insects do provide a food source to some humans and were a food item approved under the Judaic law of biblical times. Of course, the spectacular swarms do provide interesting material for National Geographic. However, W. Conner Sorensen, author of a book about the history of entomology called "Brethren of the Net" adds another benefit for these insects. Sorensen states that the establishment of the Entomological Commission was due to ravages of the migratory locust, called the Rocky Mountain locust, and that this commission marked a turning point in the scientific organization within the U.S. federal government.

So what did members of the landmark Entomological Commission learn or do? Well they learned that there was a specific breeding ground for the migratory phase of the insects and that weather patterns affected buildup and movement. What the commission did other than provide information is an open question, even though a few years later the Rocky Mountain locust ceased to be a problem in the United States. In fact, the insect can no longer be found and is thought to be extinct.

So, why have all the locusts gone? No one knows for sure. The destruction of the herds of bison removed the animals that might have contributed to suitable breeding sites for locusts. Introduction of large-scale agriculture on the eastern slopes of the Rocky Mountains might have also played a role. Regardless, the Rocky Mountain locusts are nowhere to be found. And that is one pest insect that we can do without!

 

Writer: Tom Turpin
Editor: Olivia Maddox