Adults: Bird grasshoppers are closely related to the spurthroat grasshoppers and likewise have a spur/spine on the underside of the thorax, directly behind their head. However, they are substantially larger than most spurthroat grasshoppers. Adults range between 40 and 70 mm long. They are slender grasshoppers with long wings. Adults usually have a light-colored dorsal stripe extending from the front of the head through the tegmina along the grasshopper’s back (Fig. 1). Another characteristic of bird grasshoppers is that the mesosternal lobes on the underside of the thorax are longer than they are wide (Fig. 2). The most common plains species can be differentiated as follows:
S. nitens: brownish-gray overall, lacking the distinct patterns of S. americana (Fig. 5). Adults have one light bar on the side of the pronotum.
S. obscura: olive green body with contrasting brown tegmina. Adults with a bright yellow stripe extending along the back.
S. lineata: similar to S. obscura but more variable in color, ranging from brown to green with a bright yellow and black aposematic form found in Texas. Unlike S. obscura, generally little contrast between the body and the tegmina, often with pale speckling on the pronotum.
Collectively, the four species of Schistocerca regularly found in rangeland (Schistocerca americana, S. lineata, S. obscura, S. damnifica, and S. nitens) range extensively throughout the United States. Each one occupies a more specific area, as discussed below. As all these species are strong fliers, most have scattered records from outside their typical ranges.
S. americana: most abundant in the southeastern quadrant of the United States, regularly found as far west as eastern New Mexico and as far north as Nebraska, extending to New York in the northeast. Found in a variety of open, savanna, and wooded habitats.
S. nitens: a southwestern species, ranging from Texas and Oklahoma through the central valley of California. Found in a variety of open habitats, often on trees or shrubs.
S. obscura: similar to S. americana, ranging from the southeast through Maryland, westward to New Mexico, north to Nebraska. Another generalist of open areas, it is most abundant in the southern Great Plains.
S. lineata: throughout the United States, absent from only the southeast and the northern plains states. Usually associated with sandy soils in the eastern portion of its range but more of a generalist of open habitats in the west.
S. damnifica: similar to S. americana but extending west only to central Oklahoma and Texas and only as far north as southern Illinois and Maryland. A forest-associated species but may be found in rangeland where it borders woodland.
S. americana in particular often causes problems in citrus orchards. During outbreaks, which usually follow warm winters, the grasshoppers can defoliate young trees and other crops. Most of the damage done by Schistocerca is caused by the 3rd-5th instars, which are typically more gregarious than the adults causing damage to be more concentrated. It should be noted that extreme environmental conditions can cause species that are typically solitary to occur at much higher densities and behave gregariously. This occurred with S. obscura during the 1930s during extreme drought. This trait could lead to outbreaks of Schistocerca in the future (see more under “Population ecology”).
Bird grasshoppers feed on a wide range of plants including a variety of grasses, herbaceous plants, and woody vegetation. They have been noted to feed on crops including citrus, corn, wheat, cotton, oats, peanuts, and rye where they occasionally cause economic damage. S. lineata is often found on legumes, with varying food preferences throughout its range.
Flushed grasshoppers fly considerable distances, often landing high in a tree or shrub if one is nearby. As strong fliers that can survive in a variety of habitat types, many species have scattered records far beyond their typical range (e.g., S. nitens in Nebraska and S. americana in central Wisconsin). A few species exhibit swarming behavior, such as S. americana. These swarms will often fly substantial distances to locate food. Schistcerca nitens has been observed in large numbers at lights.
Hatching is staggered in the southern parts of many species’ ranges. In Florida, eggs of S. americana hatch after 3-4 weeks. However, many species spend much more time as an egg in locations where the egg overwinters. Schistocera obscura is noted as staying as an egg for approximately 260 days under natural conditions (eggs laid in September, hatching in May).
One notable aspect of nymph development in bird grasshoppers is that development is affected by crowding. Schistocera americana, under normal conditions has six instars, while nymphs that develop under low densities may only have five. Nymph coloration is also affected by density, with nymphs being more green at low densities but more brightly colored, with patterns of yellow, orange, and black, at high densities. Nymphs typically feed in groups in the earlier instars, becoming more solitary as they age. Development from hatching to adulthood takes approximately 46–52 days in S. obscura, with nymphs developing faster at higher temperatures.
Reproduction in Schistocerca varies throughout their range and among the different species. Schistocerca americana is noted as having two broods per year in the southern part of its range, with eggs being laid in the spring and fall. The hatching time of the eggs is staggered, and the adults are long-lived, so it is possible to find adults all year long. Schistocerca nitens is similar, and in the southern parts of its range is abundant throughout the year. Further north, Schistocerca have a typical one-year lifecycle, with eggs overwintering and the adults dying toward the end of autumn. In S. americana, females are known to lay up to three egg clusters, each containing 60–80 eggs. Schistocerca obscura also laid multiple clutches but each egg cluster had substantially fewer eggs than the previous one. In S. obscura, females typically mated 18 days after their final molt, waiting another 44 days before oviposition.
Populations of bird grasshoppers can vary greatly from year to year. One notable trait of bird grasshoppers is that some species, such as S. lineata, display density-dependent aposematism, in which nymphs that develop in high densities develop brighter colors and behave more gregariously than those that develop in low densities. This is similar to the behavior in the closely related the desert locust, Schistocerca gregaria, of Africa, which gives rise to immense swarms.
Interestingly, the ability to become gregarious and swarm may be found in all Schistocerca if they reach the appropriate densities. During the dust bowl of the 1930s, S. obscura, which is typically not economically important, formed swarms that caused considerable damage throughout the Great Plains. It appears that prolonged extreme weather conditions can cause the normally solitary grasshoppers to form unusually high densities, and transition into being migratory. As extreme weather conditions become more frequent and more severe, it is possible migratory locust behavior will develop in species that currently do not display this trait.
Oklahoma State University, July 2020 by Alexander Harman
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