Species Melanoplus spretus - Rocky Mountain Locust

Rocky Mountain grasshopper, hateful migratory locust, hateful grasshopper, Kansas grasshopper, criquet des montagnes rocheuses (French)

Melanoplus spretus (Walsh) S.H. Scudder, 1878

Species name spretus is Latin, meaning despised. Locust is from Latin, locus ustus, meaning "burnt place", alluding to denuded landscapes left by locusts (1).

30-36 mm (head to tip of wings) (2)

body length 25 mm (male), 28 mm (female) (Scudder, 1898)

A long-winged and rather dull-patterned Melanoplus, notable for its fantastic swarms and damage to agriculture. It was one of the most abundant large insects in North America (and the world), but is now believed to be extinct. Historical illustrations can, perhaps, give some feeling for the living organism:

  

This living female Melanoplus (likely sanguinipes) from Wisconsin is said to resemble spretus--see comments there:

Apparently M. spretus was known mostly (or only?) as long-winged gregarious phase individuals, while these are only rarely seen in the similar M. sanguinipes, for instance. Definitive differentiation from other Melanoplus requires/required examination of genital structures of the male:

  

Formerly resident in northern Rocky Mountain region of western North America, with episodic, and agriculturally devastating invasions southward and eastward into the Great Plains. Notable invasions occurred through the 1870's, but the species declined precipitously in the last decades of the 19th century. The last living specimens were seen in southern Canada in 1902 (collected by Norman Criddle near Wawanesa, Manitoba), and the species is now believed to be extinct (1). Historical maps show former breeding and irruptive ranges:

  

Had a remarkable life cycle, with sedentary and migratory phases. One generation per year. Migratory swarms of immense size were documented in the upper Midwest in the 1870's. One 1875 swarm ("Albert's swarm") in Nebraska was documented with the aid of telegraphed reports and estimated to be 110 miles (180 km) wide by 1,800 miles (2,900 km) in length. This gives an area of 198,000 square miles (500,000 square km), larger than the state of Colorado. This swarm contained perhaps three trillion (3,000,000,000,000) individuals (1).

Extinction (or not) and causes

There is still some debate as to whether the species is truly extinct. For one thing it is difficult to believe that it just vanished. Some cite control measures as being responsible, but this is unlikely to have exterminated all populations everywhere. A recent hypothesis is that agricultural activity and habitat alteration in the permanent habitation zone of the species disrupted oviposition sites in riparian habitats (Lockwood DeBrey, 1990; Lockwood, 2004). Certainly one cannot resist an analogy with the Passenger Pigeon, a swarming bird that seemed to breed successfully only in gigantic flocks, and whose population collapsed suddenly, perhaps due to persecution in its concentrated breeding areas. Other factors may have been important in the downfall of the locust, such as the demise of the American Bison and the American Beaver at roughly the same time. Suppression of prairie fires may also have had some effect on the species.

Relationship to other species of Melanoplus

The similarity to M. sanguinipes is very great, and it is likely that specimens would not be noticed and recognized outside of the context of their swarms, especially since the non-migratory phase may look more like the "average" M. sanguinipes. It has also been suggested that M. sanguinipes IS the non-migratory phase of M. spretus, and that the genitalia might be somewhat different in the two phases. However, no proof has been offered of this, and rearing experiments have indicated that migratory phase M. sanguinipes (which look similar to migratory M. spretus) have genitalia characteristic of M. sanguinipes and not like M. spretus. In addition, genetic/molecular studies of Melanoplus spretus specimens have supported the validity of the species. Indeed, the molecular studies suggest that the M. spretus may have been more closely related to Melanoplus bruneri than to M. sanguinipes (Chapcoa and Litzenbergerb, 2004). At any rate, absent proof that M. spretus still exists, it is generally presumed to be extinct.

Economic and ecological effects

There are a few other grasshopper species in North America that swarm on a local scale, and also some that have something similar to a migratory phase (produced under crowded conditions), but none of those has ever been recorded as producing massive migrations even remotely comparable to those of M. spretus. The extinction of this species left North America without a "locust" that swarms in devastating numbers, which has no doubt been a boon to agriculture. However its loss may have had detrimental effects on other species--the locust was an important food source for the (now extinct) Eskimo Curlew. The curlew declined in numbers as the locust died out, though the loss of the locust was likely one of several factors in the extinction of the curlew (Cornell University, All About Birds--Eskimo Curlew).

Historical references: