Rocky Mountain Locust, an insect belonging to the same family (locustidae of West-wood, acrididae of later authors) as the locusts of the old world and of Scripture. It is the only species in this country, E. of the Rocky mountains, that has the same migratory habit and great power for harm which characterizes those whose ravages are described by the prophet Joel, and which have figured so largely in the history of southern European and Asiatic nations. A species often complained of on the Pacific slope is probably the same, or a variety of the same. The Rocky mountain locust, first specifically characterized by Prof. Cyrus Thomas, in his "Acrididae of North America" (1873), as caloptenus spretus, is popularly known as the grasshopper, a term loosely applied to most large hopping insects. During 1873, 1874, and 1875 this insect attracted unusual attention, and in the unprecedented amount of injury and suffering which it entailed on the farmers of the west it proved a national calamity. In 1873 Minnesota and Iowa were sorely scourged by it in their western counties, and had to appeal to the nation for assistance to relieve the consequent suffering; in 1874 Nebraska and Kansas suffered to such an extent that the efforts of the state authorities and the contributions of people from all parts of the Union were insufficient to prevent a vast amount of distress; while in the spring of 1875 parts of Missouri and Kansas were again terribly smitten.
It has been estimated that $50,000,000 would not cover the loss occasioned to the country by this insect during these three years. The species measures on an average about 1 1/3 in. from the head to the tip of the closed wings, and the wings extend about one third their length beyond the tip of the abdomen. The color is variable, but the more common specimens are yellowish white beneath; glaucous across the breast and about the mouth parts; pale bluish glaucous, often with shades of purple, on the sides of the head and thorax and on the front of the face; olive-brown on the top of head and thorax; pale beneath, more or less bluish above and marked with black, especially toward base, on the abdomen. The front wings have the ground color pale grayish yellow, inclining to green, and their spots and veins brown; the hind wings, except a yellowish or brownish shade at apex and along the front edge and a green tint at base, are transparent and colorless, with the veins brown. The front and middle legs are yellowish. The hind legs have the thighs striped with pale glaucous and reddish on the outside and upper half of inside, with four broad black or dusky marks on the upper edge, the terminal one extending beneath around the knee.
The shanks are coral-red with black spines; the feet somewhat paler, with black claws; antennae pale yellow; palpi tipped with black. In the dead specimens all these colors become more dingy and yellow. It very closely resembles, and is often confounded with, the red-legged locust (caloptenus femur-rubrum, De Geer), a species common to the whole central portion of the continent from the Atlantic to the Rocky mountains, which, though capable of short flights, never commits the same havoc. This last is, on an average, smaller, darker, with shorter and less conspicuously spotted wings (seldom extending more than one sixth of their length beyond the tip of the abdomen), and the last abdominal joint of the male is bluntly cut off at the top, and not tapering and notched as in spretus. There is a third species, caloptenus Atlantis (Riley), occurring more particularly in the mountain regions of the Atlantic, which in many respects is intermediate between the two, and which often migrates in large swarms from place to place, and proves injurious during very hot dry years. All three approach each other so closely through divergent individuals that entomologists are at variance as to whether they should be considered distinct species, or mere varieties or geographical races of the same species.
But compared with the Rocky mountain species, the Others are harmless. This species seems to be subalpine by nature, and to breed and flourish only in the high plains and plateaus of the Rocky mountain region; and Prof. C. V. Riley is of opinion that those which devastated S. W. Dakota, Nebraska, Kansas, and the western portions of Minnesota, Iowa, and Missouri (in all of which country the species is not indigenous), come principally from the mountain regions of Wyoming, Dakota, Montana, and British America. According to his seventh annual "Report on the Insects of Missouri," "the insect is at home in the higher altitudes of Utah, Idaho, Colorado, Wyoming, Montana, N. W. Dakota, and British America. It breeds in all this region, but particularly on the vast hot and dry plains and plateaus of the last named territories and on the plains W. of the mountains; its range being bounded, perhaps, on the east by that of the buffalo grass. William N. Byers of Denver, Colorado, shows that they hatch in immense numbers in the valleys of the three forks of the Missouri river and along the Yellowstone, and how they move on from there, when fledged, in a S. E. direction at about 10 m. a day.
The swarms of 18.67 were traced, as he states, from their hatching grounds in W. Dakota and Montana, along the E. flank of the Rocky mountains, in the valleys and plains of the Black hills, and between them and the main Rocky mountain range. (See Hayden's "Geological Survey of the Territories," 1870, pp. 282-3.) In all this stretch of country, as is well known, there are vast tracts of barren, almost desert land, while other tracts for hundreds of miles bear only a scanty Vegetation, the short buffalo grass of the more fertile prairies giving way, now to a more luxurious vegetation along the watercourses, now to the sage bush and a few cacti. Another physical peculiarity is found in the fact that while the spring on these plains often opens as early, even away up into British America, as it does with us in the latitude of St. Louis, yet the vegetation is often dried and actually burned out before the first of July, so that not a green thing is to be found. Our Rocky mountain locust, therefore, hatching out in untold myriads in the hot sandy plains, 5,000 or 6,000 ft. above the sea level, will often perish in immense numbers if the scant vegetation of its native home dries up before it acquires wings; but if the season is propitious and the insect becomes fledged before its food supply is exhausted, the newly acquired wings prove its salvation.
It may also become periodically so prodigiously multiplied in its native breeding place that, even in favorable seasons, everything green is devoured by the time it becomes winged. In either case, prompted by hunger, it rises in vast clouds in the air to seek for fresh pastures. Borne along by the prevailing winds that sweep over these treeless plains from the northwest, often at the rate of 50 or 60 m. an hour, the darkening locust clouds are soon carried into the more moist and fertile country to the southeast, where they fall upon the crops like a plague and a blight. Many of the more feeble or of the more recently fledged perish, no doubt, on the way; but the main army succeeds, with favorable wind, in bridging over the parched country which offers no nourishment. The hotter and drier the season, and the greater the extent of the drought, the earlier will they be prompted to migrate, and the further will they push on to the east and south." These vast flights never extend E. of a line drawn at a rough estimate along the 94th meridian; nor do they remain permanently in the low Mississippi valley country.
The sudden change from the attenuated and dry atmosphere and general climatic conditions of 5,000 or 6,000 ft. above the sea, to the more humid and dense atmosphere of 1,000 ft., affects them injuriously, and they either leave, die, or disappear through degeneration or miscegenation, until no trace of them is left by the second or third generation. These incursions into the more fertile country to the east occur at irregular intervals, and are most frequent in the country toward the northwest, nearest the native home of the species. Thus, locust ravages are more to be feared in Colorado and W. Minnesota than in Missouri or Texas. A chronological study of these incursions shows that there have been during the present century only three as extended as that of 1874, when the insects reached into the western counties of Missouri. But we find records of a dire visitation in Guatemala as far back as 1632, in Gage's "West Indies," and the early Jesuit missionaries of California have left numerous records of locust injuries on the Pacific coast during the present and preceding centuries. - The natural history of the Rocky mountain locust is similar to that of all true locusts.
The female is furnished at the end of her abdomen with two pairs of horny valves, which open and shut, and which enable her to drill a hole in the ground in which to deposit her eggs. These, to the number of from 60 to 100, are voided in a glutinous fluid, which hardens and holds them together, and which, in combination with particles of earth, covers them with a sort of pod. The eggs are deposited in the invaded country during the latter part of the growing season, and while some few may hatch prematurely the same season, the great bulk of them do not hatch till the following spring. The young locust has the general characteristics of the mature insect, and differs principally in lacking wings. After shedding its skin at four different periods, the wings are acquired in from six to eight weeks from the time of hatching. It is doubtful whether in their native home the insects show any tendency to migrate except when forced by necessity. They are sluggish in the cooler parts of the day, and fly principally between the hours of 10 A. M. and 4 P. M., and then only when the wind is in the direction they wish to go. Their life is limited by the spring and autumn frosts, and all that hatch in the spring perish at the approach of winter, soon after the eggs are laid.
The young "hoppers " in the invaded country often abound to such an extent that they totally destroy all crops. In the spring of 1875, in several of the western counties of Missouri, especially in the middle portion of the state, and in the adjacent part of Kansas, the ground was kept as bare as in midwinter for nearly two months after spring opened, nothing green being left but the leaves on the forest trees, and a small glossy-leaved plant, the amarantus blitum, which they invariably left untouched. When not too hard pressed for food, they will pass by most species of milkweed (asclepias), as also the wild grass on low prairies. The distress caused by these insects in the part of Missouri mentioned, combined with previous short crops from drought and the chinch bug, made public measures of relief necessary; and, although the state entomologist insisted that the infliction was temporary and limited to its present area, many persons emigrated, and a day of fasting and prayer was appointed by the governor. These young hoppers travel during the hotter hours of the day in immense schools, not in any particular direction, but in search of food. They walk and hop alternately, moving at the rate of about three yards a minute.
Toward evening they go to feeding, and generally collect afterward on fences or other objects away from the ground, so as to avoid moisture. As they grow older their numbers are continually reduced, not only by the attacks of enemies and by climatic influences, but by devouring one another; for when they are swarming to so unnatural an extent this cannibalistic propensity is fully developed. Those which acquire wings instinctively go toward their native home, or in the direction whence their parents had come the previous year. This exodus begins in Missouri early in June, and reaches its acme about the middle of that month. They generally leave in time to enable the farmers to raise a good crop of corn and of most vegetables. Indeed, the distress and devastation is not unfrequently followed, as in 1875, by great abundance. The incursions generally take place after two or three years of excessive drought, and are likely to be followed by a comparatively wet season. Aside from this somewhat uncertain cause, the total destruction of the vegetation during the first six or eight weeks of spring well nigh exterminates many other insect pests, such as the chinch bug; and the manure left by the locusts, in the very best condition to be appropriated, increases in many cases the fertility of the soil.
Not only is there no danger of this plague ravaging the country E. of the 94th meridian, but there is none of its becoming a permanent evil in any part of the Mississippi valley proper.
Fig. 1. - Rocky Mountain Locust (Caloptenus spretus).
Fig. 2. - Red-legged Locust (Caloptenus femur-rubrum).
Fig. 3. - Anal Characters of Male of Rocky Mountain Locust: a, side view of tip; 6, c, hind and top views.
Fig. 4. - Anal Characters of Male of Red-legged Locust: a, side view of tip; b, c, hind and top views.
Fig. 5. - Anal Characters of Female of Rocky Mountain Locust, showing horny valves.
Fig. 6. - a. Female depositing eggs. &. Egg pod with end broken open. c. Eggs. d, e. Earth partially removed, showing an egg mass in place and one being placed. f. Place where such a mass has been covered up.
Fig. 7. - a, a. Newly hatched larvae, b. Full-grown larva. c. Pupa.
Some curious changes often follow the wake of these locusts, where they denude a country of its vegetation. Thus, the common purslane gets a start over other weeds, and the large green and black larvae of a common and pretty hawk moth (deilephila lineata), which feed upon it, abound to such an extent as to frequently cause unnecessary alarm. But the most striking change is the appearance of a fine grass unnoticed during ordinary seasons, which furnishes abundant and nutritious food for stock. This grass is the vilfa vaginoeflora, an annual which is common from the Atlantic to the Rocky mountains. The locusts kill out the blue grass by gnawing it down too closely, and the changed conditions give the vilfa temporarily the advantage in the struggle for existence; but in a year or two the normal relations between species are restored. - The parasites which aid man in subjugating this locust consist mainly of four species, two mites and two flies. The silky mite (trombi-dium sericeum), a small scarlet animal about two lines long, attacks the egg underground; while the locust mite (astoma gryllaria), a still smaller species, of similar color, fastens in numbers on the body at the base of the wings of the mature insect.
The anonymous tachina fly (tachina anonyma), an insect twice as large as a house fly but somewhat resembling it, fastens its eggs to both the young and the mature locusts; the maggots hatched from these penetrate the body and devour the vitals of their victim, soon causing its death. Finally the common flesh fly (sarcophaga earnaria) deposits living maggots under the wings of the locust, which also in time succumbs to them. - A partial remedy against the locust, in regions where it is not indigenous, is found in natural agencies. Climatic conditions are often unfavorable, and many animals and insects prey upon it. Almost all the birds of the western plains feed upon the locust and its eggs. The protection of the prairie chicken and quail would be an excellent measure. A better means of preventing its ravages is the destruction either of the eggs or of the unfledged young. The eggs being laid in masses just beneath the surface of the soil, usually on high, dry ground, simple harrowing or shallow ploughing will break up the masses and expose the eggs to the desiccating and bleaching effects of the atmosphere, which are fatal to them. If deeply turned under by the plough, many of the eggs will rot, and the rest will hatch too late for the young to do serious damage.
Ground thus treated should not be turned again in the spring. A few days' excessive moisture is also fatal to the eggs, and where irrigation is practised they may be very easily destroyed. The eggs, however, are often placed where none of these means can be employed. After hatching, the young hoppers may be destroyed by heavy rolling, by collecting them into heaps and burning them with coal oil, or into windrows of straw, which is then set on fire. The most effectual way of destroying them is by ditching, especially where there is no hay or straw in which to burn them, as in western Missouri in 1875. A ditch 2 ft. wide and 2 ft. deep, with perpendicular sides, 4s an impassable barrier to the young insects. They tumble in, and as they accumulate die at the bottom. To prevent the intolerable stench, pits or side ditches should be dug into which they may be swept and buried. Hogs and poultry may also be turned out to feed upon them. Prof. Riley urges as a possible means of preventing locust incursions, that a thorough study of the insect in its Rocky mountain breeding places be made by the national government; for "by learning just when and how to strike the insect so as to prevent its undue multiplication there, . . . we may hope to protect the fertile states to the east from future calamity." - From time immemorial locusts have been used as food in oriental countries, and it has been found that the Rocky mountain species makes a very good soup or bisque.
Fig. 8. - Locust Mite, greatly enlarged.
Fig. 9. - Silky Mite. Natural size at side.
Fig. 10. - Sarcophaga carnaria: a. Larva. b. Pupa. c. Fly. (The hair lines show average natural lengths.) d. Enlarged head and first joint of larva, showing curved hooks, lower Up (g), and prothoracic spiracles. e. End of body of same, showing stigmata (f) and prolegs and vent. h. Tarsal claws of fly, with protecting pads. i. Antenna of same, enlarged.