Psoloessa delicatula

Distinguished from similar slant-faced grasshoppers by combination of: pronotum with median carina cut once (not entire), lateral carinae deeply cut and depressed at constriction; ivory-colored oblique ridge on lower rear of lateral pronotal lobe; triangular marking on upper marginal area of hind femur; and orange distal hind tibia. Nymphs identifiable by curved brown stripes on vertex, filiform antennae, and distinctive pale yellow oblique ridge on lower rear of lateral pronotal lobe (becoming more prominent in later instars). Compare with Phlibostroma quadrimaculatum and other Gomphocerinae: P. delicatula lacks the four spots of P. quadrimaculatum and shows the unique ivory ridge pattern.

Adults are small (males ~99 mg live weight, females ~284 mg), with dull gray-brown coloration and dark brown spots and maculations. Head has slightly slanted face with grooved frontal costa and well-defined square to oblong lateral foveolae. Pronotum has distinct median carina cut once in front of middle; lateral carinae constricted in middle, deeply cut, and strongly depressed at cut region. Lateral pronotal lobes display a rounded broad ridge running diagonally upward and a smaller oblique ridge below, often conspicuously ivory-colored. Hind femur bears triangular marking on upper marginal area; hind tibia pale gray with brown spots proximally, orange distally. Nymphs pale tan to brown with dark brown markings and light dorsal band from head to abdomen tip; older instars darken to brown-gray.

Inhabits grasslands of western North American states and provinces, specifically desert shortgrass, mixedgrass, and bunchgrass prairies. Extends into western desert shrub communities where grasses form sparse understory. Present in foothill habitats up to 8,076 feet elevation. Absent from mountain grasslands. Requires habitats with grass cover for shelter and thermoregulation.

North America: western United States and Canada. Documented in British Columbia, Colorado, New Mexico, and Texas. Core range spans western plains and intermountain grasslands from Canada through the western United States.

Adults present May through June and into summer. Nymphs hatch early July in northern Colorado, with development extending through summer and fall; overwinter as fourth and fifth instars, resume activity April, reach adulthood April-May. In southern range, eggs may hatch same summer as laid. Mating observed 9-11 a.m. in June and early July.

Feeds almost exclusively on grasses and sedges. Early spring nymphs consume needleleaf and threadleaf sedges plus cool-season grasses (western wheatgrass, downy brome, sixweeks grass). Adults shift to warm-season grasses, especially blue grama and sand dropseed. Documented feeding on two sedge species and 14 grass species. May ingest minute amounts of forbs, lichens, moss, and arthropods.

Life cycle one to two years depending on latitude. In central Saskatchewan and northern range: two-year cycle with eggs laid summer, remaining viable but unhatched until second summer. Eggs deposited 0.75-1.25 inches deep in soil; hatching period lasts 2-6 weeks. Nymphal development ~120 days; overwinter as nymphs under ground litter, shallowly buried. In southern range: eggs may hatch same summer as laid. Gravid females oviposit in bare soil, boring over 1 inch deep, depositing 18 eggs with minimal froth, forming 0.75 inch froth plug; entire pod ~1.5 inches. Eggs yellow, 4.9 mm long.

Ground-dwelling with elaborate thermoregulatory repertoire. Basks 3-4 hours after sunrise, orienting body perpendicular to sun; requires soil temperatures of 70-75°F to begin normal activity. At air temperatures above 77°F, moves to shade; above 90°F, actively seeks shade and assumes 'straddle' posture with hindlegs spread from body. Six described thermoregulatory postures include 'squat' (body and flexed hindlegs lowered to substrate). Lowers abdomen toward ground and moves hindlegs away from body for cooling. Evasive flights silent and sinuous, 5-9 feet at 4-6 inches height, ending with quick turn and sudden drop; lands horizontally, may face intruder. No documented migration. Males stridulate with 2-4 acoustical signals when approaching females; rejected males may be repelled by female's ticking sounds from hind tibiae striking tegmina.

Primary consumer in grassland ecosystems. Contributes to nutrient cycling through herbivory on grasses and sedges. Serves as prey for various predators; evasive flight behavior suggests predation pressure. Early-season activity makes it one of first grasshopper species causing measurable rangeland damage in spring.

Minor rangeland pest. Populations normally 0.5-1 adults per square yard cause no significant damage. Outbreak densities of 25-30 per square yard in mixedgrass prairie cause early-season grass damage; infested sites may cover up to 4 square miles. Outbreaks can persist 3+ years. Quantitative damage assessment not undertaken. Subject of ecological research on thermoregulation and life cycle flexibility.

• Phlibostroma quadrimaculatumBoth in Gomphocerinae with slant-faced morphology; P. quadrimaculatum has four distinct spots on tegmina versus spotted/maculated pattern of P. delicatula, and lacks the ivory oblique ridge on pronotal lobe.
• Psoloessa texanaCongener with similar size and habitat; P. texana has different pronotal carination and coloration patterns, and occupies more southerly range with different seasonal phenology.

• grasshopper
• slant-faced grasshopper
• thermoregulation
• rangeland
• grassland
• pest
• North America

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• Grasshoppers of Colorado
• Grasshoppers of Colorado
• Species Records and Accounts
• Brownspotted Grasshopper
• Grasshoppers of Colorado
• List of Species Fact Sheets| Grasshoppers of Wyoming and the West