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The largeheaded grasshopper ranges widely in the grasslands of North America. Preferring a habitat of tall, lush grasses, it is often the dominant grasshopper species in the tallgrass prairie and is a common inhabitant in taller types of the mixedgrass prairie. In shorter types it may be locally abundant in patches of tall grass growing in swales, ravines, along streams, and in roadsides.
The female weighs twice as much as the male. Live weights of males collected from the mixedgrass prairie of southeastern Wyoming averaged 206 mg and females averaged 419 mg (dry weights: males 63 mg, females 137 mg).
Extensive laboratory feeding tests reveal that largeheaded grasshoppers surprisingly prefer several species of grasses and forbs to their usual host plants. The preferred plants in the laboratory include the grasses: downy brome, Scribner panicum, barnyardgrass, witchgrass, junegrass, and foxtail barley; and the forbs: dandelion, meadow salsify, and skeletonweed. Plants as acceptable as the natural host plants include green bristlegrass and smooth brome, both introduced species. Smooth brome grows profusely in roadsides and often harbors dense populations of the largeheaded grasshopper. Less attractive grasses include blue grama, buffalograss, sand dropseed, needleandthread, prairie sandreed, and Kentucky bluegrass. The latter grass, however, is ingested in considerable amounts when it occurs in the habitat.
In tall, lush grasses, the largeheaded grasshopper rests vertically head-up on the host plant. During feeding, it may remain in this position or it may turn around and face vertically head-down. In either orientation it eats the edge of the leaf, creating a long gouge along one side and leaving a narrow edge of the leaf intact. The feeding of a nymph (instar IV) on western wheatgrass resulted in a 30 mm long, 2 mm wide gouge in the middle of the leaf, with 1 mm wide edge left standing. As soon as a head-down individual finishes a feeding bout, it turns around and again rests vertically head-up.
The less common long-winged adults have strong powers of flight and no doubt are able to disperse considerable distances. Perhaps during past times, development of large numbers of long-winged adults with subsequent dispersal resulted in the widespread geographic range of this species.
The nymphs are distinguishable by their structure, color, and shape (Fig. 1-5).
1. The head is large relative to the rest of the body, face is slanted; antennae are filiform; fuscous vertical stripe below and horizontal stripe behind compound eye, both stripes contrasting noticeably with light gray of head; compound eye brown with white to pale tan spots.
2. Edge of pronotal disk with fuscous wedge-shaped stripe, wide anteriorly, narrowing posteriorly, faint in instar I.
3. Hind femur with pronounced dorsal stripe that extends into ventral half of medial area; hind tibia pale yellow with front fuscous in instars I to III, blue in instars IV and V.
Little is known about the maturation and reproduction of this grasshopper in nature. Laboratory cage tests suggest a high rate of fecundity. Short-winged females produced 120 eggs per capita during a reproductive period experimentally set at 25 days. Long-winged females produced fewer eggs because of the apparent necessity to divert part of the nutrient intake to the production of flight muscles and long wings.
No observations of courtship have been made, and published observations of mating are zilch. One mating pair was seen in the mixedgrass prairie of eastern Wyoming at 9:15 a.m. DST on 1 August 1968 and another in a roadside habitat dominated by smooth brome and western wheatgrass at 9:30 a.m. DST on 26 August 1993. In the latter case, the pair, which was basking vertically head-up 6 inches high on a smooth brome leaf, had assumed the usual mating position of grasshoppers (i.e., the male clinging on top of the female). The male's head rested immediately behind and above the female's. Because of the smaller size of the male, the female's genitalia had to curve up to meet the male's curving down.
The oviposition sites selected by females are uncertain. In a published study of grasshopper biology conducted in the sand prairie of southeastern North Dakota, females were said to oviposit in vegetated sites. However, it is not clear whether the females oviposited into or close to crowns or into small bare areas interspersed among the plants. The egg-laying behavior of females confined in a laboratory terrarium of sandy loam soil and mixedgrass prairie turf further confuses the issue. During ten days of confinement, five short-winged females deposited five pods in the bare soil and none in the turf.
The pods are 1 to 1 1/4 inches long and slightly curved in the region of the eggs (Fig. 10). The pods of short-winged females usually contain 28 eggs, equalling the total number of ovarioles, while the pods of long-winged females usually contain from 20 to 24 eggs. Eggs range in color from olive to brownish yellow and measure from 4.1 to 4.4 mm in length.
The distribution of the largeheaded grasshopper extends west into the mixedgrass prairie, where the species occupies the more luxuriant aspects, particularly swales, riparian areas, and roadsides. In these sites, stands of western wheatgrass grow tall and rank, providing favorable habitats and an abundance of food. Populations aggregate in these habitats reaching densities as high as 12 young adults per square yard and often achieve dominance in the grasshopper assemblage. In contrast, surrounding mixedgrass prairie usually harbors less than one young adult per square yard, and the species occupies a low rank in the assemblage.
This grasshopper inhabits other grasslands of the West, usually in limited areas and at low densities. In the shortgrass prairie the species is rarely a member of the grasshopper assemblage, but in northwestern Texas it was a common species on rangeland in two out of seven years (1966-72). The desert prairie does not often harbor the largeheaded grasshopper, but south of Tucson in an ungrazed sanctuary of the Audubon Society it inhabits level uplands covered by luxuriant stands of blue grama, plains lovegrass, and wolftail grass. Average seasonal densities from 1985 to 1989 ranged from 0.1 to 0.3 per square yard. In 1989, at 0.3 per square yard, the largeheaded grasshopper became the dominant species in a low-density assemblage of nine species. This grasshopper is rarely found in sites of the bunchgrass prairie, but in Idaho it is one of the major species living on steep hillsides vegetated with bluebunch wheatgrass. Densities, however, are low, usually less than one per square yard.
In the morning on a clear day, two to three hours after sunrise, the nymphs and adults, resting vertically head-up on tall grasses, begin to bask by turning a side perpendicular to the rays of the sun and lowering the associated hindleg. This orientation raises their body temperature, which has fallen during the night, to that of the habitat, which in Wyoming ranges from 50 to 60½F. They remain quietly basking, occasionally stirring, for two to three hours and eventually become active in mid morning. Individuals in habitats of short and mid grasses usually spend the night under litter. In the morning they bask sitting horizontally on bare ground.
After basking, the grasshoppers infrequently move about on the tall grasses by crawling or jumping from one plant to another. They may also back down a grass stem or turn around and crawl head-down to reach the ground. On the ground they crawl and hop intermittently, moving a net distance of 15 feet in 30 minutes. Grasshoppers perched on tall grass have been observed to feed from early morning to evening (7 a.m. to 6 p.m. DST). More observations of feeding, however, have been made from 9 to 11 a.m. DST than during any other two-hour period.
A second period of basking occurs in late afternoon. At this time the grasshoppers bask for approximately two hours. Near sunset, when shadows engulf their habitat, they take nighttime positions. Those basking vertically head-up on tall grasses may remain there, or back down several inches, while others may find shelter under ground litter.
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