Did the Rocky Mountain Locust Infest Southeastern North America During the Pleistocene?

The first frosts of fall are about to end the lives of most adult insects here in Georgia.  Before we say goodbye (and in some cases good riddance) to the denizens of the insect world, let’s consider a couple of interesting species.

We’ve all heard of comically cheap horror movies such as “The Monster that ate Toledo,” but the Rocky Mountain locust literally did eat great swaths of the midwest during several 19th century invasions when they consumed farmer’s crops, every blade of grass, all the leaves of trees and shrubs, fence posts, carrion, hanging laundry, sheep’s fleeces, leather shoes, and each other.  The natural world humbled our pioneer ancestors. However, no specimen of this species (Melanoplus spretus),  the swarming phase of the short-horned grasshopper, has been collected since at least 1899–an astonishing extinction because an 1875 swarm estimated to be in the trillions and covering a territory the combined size of New England and the mid-Atlantic states descended upon the midwest and devastated farmer’s crops.

Top: Illustration of the short-horned grasshopper.  Bottom:  Illustration depicting farmers’ futile attempts to stop these locusts from destroying their wheat fields.

Laura Ingalls Wilder, author of the Little House series, gives an account of this disaster in her book, On the Banks of Plum Creek.  Her father had bought a nice frame house and planted a field of wheat–both on credit.  He did this as a gift for his wife so she wouldn’t have to continue living in a sod house with a dirt floor.  Laura reported that one day a cloud of locusts appeared in such large numbers they blocked out the sun.  They settled on her father’s wheat field and destroyed his crop, forcing him to leave home for six months in order to earn money as a laborer and pay back his loan–a sad situation, especially in the days before the telephone when the only communication was the snail-like mail.

Locust swarms were common during draught years throughout the 19th century, but apparently this insect became extinct around 1900.  Why did it become extinct?  Grasshoppers lay their eggs in the ground.  Scientists think farmers first cultivating land near the Rocky Mountains plowed the insect’s communal nesting grounds, destroying the buried eggs, and thus accidentally managed to wipe this disastrous pest into oblivion.  At first its extinction wasn’t even noticed because other species of grasshoppers took their place and did considerable damage as well.

The swarming behavior of this grasshopper species occurred only during drought years, much like that of swarming species of locust still found in Africa today.  Drought increases the nutritional content of plants by concentrating sugar and nutrients, and it weakens plant defenses.  The surviving plants exist in shrinking numbers near moist sites such as river valleys.  When these grasshoppers congregate in large numbers to feed on the shrinking number of surviving but highly nutritious plants, they begin coming into contact with each other.  Touching each other causes their serotonin levels to rise which in turn causes physical changes–they change color (turning red), they eat more, breed more, and it signals their swarming migratory behavior.

During the last glacial maximum from 28,000 BP-15,000 BP (calender years) drought conditions were prevalent in southeastern North America, and many upland sites probably consisted of scrub oak, cedar, and grass due to a dearth of lightning induced fires.  It occurred to me that this was the type of environment Rocky Mountain locusts would’ve found suitable.  The spread of closed canopy forests following the end of this severe glacial stage eliminated much of this suitable habitat east of the Mississippi.  During the 19th century, this species no longer occurred east of western Arkansas and did not penetrate the southeast.

Evidence that Rocky Mountain locusts swarmed in large numbers during the Ice Age can be found in the ice of Grasshopper Glacier located in Custer National Forest (Montana) where millions of dead mummified locusts are embedded. See the following link for a photo of one of these fossils

http://fcmdsc.wordpress.com/2010/09/17/the-rocky-mountain-locust/

Parts of swarms flew over this glacier and they succombed to the cold, dropped from the sky, and froze.  Today, global warming is causing this glacier to retreat, exposing these mummified locusts to decomposition.

In the southeast climatic conditions during the last glacial maximum were so dry that many river beds dried up, creating large amounts of exposed sand and sand bars.  Frequent winds blew this sand into large eolian sand dunes that rolled across the landscape until wetter conditions returned and plants took root and held these sand dunes down.  There are many of these sand dunes in Georgia today, such as the Ohoopee Dunes, but they’re covered in vegetation and hidden.

Many western species of vertebrates colonized what’s now Georgia, especially during the dry climate phases.  Paleontological evidence from Georgia and neighboring states show that 13-lined ground squirrels, jack rabbits, hog-nosed skunks, badgers, coyotes, prairie chickens, upland sandpipers, magpies, ravens, sharp-tailed grouse, and burrowing owls lived in the southeast.  If western species of vertebrates lived in the region, than it’s logical to assume western species of invertebrates lived here as well.  It’s likely that congregations of megafauna and locusts around shrinking waterholes during severe droughts denuded vegetation, thus contributing to the formation of eolian sand dunes.

North America’s Little Known Army Ants

Of the 150 species of army ants in the genus Neivamyrmex, only 3 are able to inhabit the climate of temperate North America with its freezing temperatures during winter.  These species are likely relics from a time previous to when the Ice Ages began to occur.  Before the Pliocene many more species of army ants likely occurred in North America for they’re believed to have originally evolved during the Cretaceous.  All 3 of the temperate species of army ants have been recorded in Georgia including Neivamyrmex carolinensis, though there are more North American species found in Texas and southern California and the southwest.

http://www.cs.unc.edu/~hedlund/playpen/ants/GenusPages/Ecitoninae/Neivamyrmex.html

I’ve seen this medium-sized, muscular-looking red ant on at least one occasion when I witnessed a dozen tearing apart an earthworm.  (I’m not an entomologist so I can’t guarantee my identification.)  The reason these species are little known is because they’re mostly nocturnal and don’t form enormous colonies, like their South American cousins.

A total of 144 species of ants have been recorded from Georgia; 218 from Florida.  There are probably many more that scientists haven’t surveyed.  Here’s a good source for indentifying ants– www.antweb.org

References:

Ipser, Reid; et.al.

“A survey of ground dwelling ants (Hymenoptera: Formicidae) in Georgia”

Florida Entomologist 87 (3) September 2004

Lockwood

Locust: The Devastating Rise and Mysterious Disappearance of an Insect

2004

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