Common name - Flabellate grasshopper (Ball et al. 1942).
Geographic distribution - found throughout the Great Plains, extending from British Columbia to Saskatchewan (Canada) and south to Arizona and Texas (Hebard, 1929; Helter, 1972). Two subspecies occur in Colorado; M. occidentalis occidentalis, which is found primarily on the eastern plains; and M. occidentalis brevipennis, which occurs in western Colorado (Alexander, 1941).
Habitat - common in open grassland areas, often extending its range above timberline (Hebard, 1928; Hebard, 1929; Helfer, 1972).
Food habits - a polyphagous feeder, exhibiting a preference toward forbes. Its preferred food plants are scarlet globemallow, western wheatgrass and side. It also feeds on bahia, blue grama and threeawn (Kumar et al., 1976, Mulkern et al., 1969).
Eggs - eggs are yellow in color. Average egg length, 5.31 mm; average diameter, 1.24 mm (Tuck and Smith, 1939).
Nymph - five instars.
Adult - small to medium in size. Color is reddish-brown. Dorsum is strongly mottled with dark backish-brown spots; light brown color underneath. Blackish-brown median stripe broadens posteriorly, passing from between the eyes to the back of the head but seldom continuing onto the pronotum. Dorsal posterior margin of pronotum is a rounded right angle. Head is yellow to yellowish-brown. Black patch is present on the upper part of the anterior half of the lateral lobes. Tegmina extend to or a little beyond the tip of the abdomen and are slender and tapering. Tegmina are brown in color with a slender, median, yellow stripe and frequently are marked with squarish, dark spots. Wings are colorless. Hind remora are variable in color with oblique pale patches on a dark background or the reverse. Hind tibiae are light blue. Cerci are large and triangular, wide at base, slightly tapering and rounded at apex. Furculae are very small and triangular. Subgenital plate has a small conical tubercle below apical edge. Male length, 18 mm; female, 25 mm (Scudder, 1897; Somes,1914).
Seasonal history - hatching occurs from late May to mid-June. Adults are present from late June to the middle of October (Newton et al., 1954).
Abundance and importance - frequently a pest of cultivated crops but usually of little economic importance on grasslands (Mulkern et al., 1969).
M. occidentalis fact sheet from the Field Guide to Common Western Grasshoppers
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