Encoptolophus costalis (Scudder)
Wyoming Agricultural Experiment Station Bulletin 912
Species Fact Sheet
by Robert E. Pfadt
Geographic range of Encoptolophus
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The dusky grasshopper ranges widely in western North America from
Canada to Mexico. The species inhabits several kinds of grasslands
including the mixedgrass, shortgrass, bunchgrass, and desert prairies.
It is most abundant in the northern mixedgrass prairie, and is the
dominant species on certain rangelands of Saskatchewan. There it favors
moist areas of rich grass and sedge growth interspersed with bare
ground. In its southern distribution, mesic swales and roadsides dominated
by western wheatgrass and prairies with Houston black clay soil dominated
by Texas needlegrass afford favorable habitats.
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The dusky grasshopper is a rangeland species that feeds on native
grasses and sedges. In the assemblage of grasshoppers inhabiting
a grassland site, it is usually a subdominant member that does little
damage by itself but adds to the damage of more serious pests. Occasionally,
in habitats favorable to the species, it becomes the dominant grasshopper.
In the Matador site of the International Biological Program (northern
mixedgrass prairie in southwest Saskatchewan), the dusky grasshopper
was the dominant species, making up as much as 74 percent of the
grasshopper population. The density, however, was low, with approximately
2.5 young adults per square yard. Estimates made from meticulous
laboratory studies of food consumption suggested that in the field
the population of grasshoppers ingested 2.4 percent of annual production
of grass in 1968 and 1.5 percent in 1969. There was a lack of apparent
damage to the vegetation such that the rather small population of
grasshoppers had no great impact on the standing crop of grasses.
The dusky grasshopper has been reported as a minor pest in alfalfa
in Arizona and North Dakota and as a pest in fall wheat in Nebraska.
In the latter case, adults migrated from depleted rangeland into
the adjacent wheat crop.
The dusky grasshopper is a medium-sized species with marked sexual
dimorphism in body size. Live weight of males averages 168 mg and
of females 468 mg (dry weights: males 50 mg, females 135 mg).
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The dusky grasshopper in its prairie habitat feeds on grasses and
sedges. Western wheatgrass and needleleaf sedge are its principal
host plants. Other plants eaten in substantial quantities include
northern wheatgrass, needleandthread, green needlegrass, and blue
grama. Analyses of crop contents of grasshoppers collected in Colorado,
Kansas, North Dakota, and Saskatchewan reveal that eight additional
grasses and one sedge are consumed in variable amounts: quackgrass,
prairie junegrass, sand dropseed, little bluestem, sideoats grama,
Kentucky bluegrass, foxtail barley, timothy, and Penn sedge.
In an unusual habitat, such as an alfalfa field or a roadside,
the dusky grasshopper may feed on a mixture of forbs and grasses.
Of 52 specimens collected from an alfalfa field in North Dakota,
30 had ingested alfalfa. In laboratory tests, starved individuals
limited to single food plants fed well on certain forbs and refused
others. Well-eaten plants included scarlet globemallow, prairie
coneflower, dandelion, and a vetch, Vicia sparsifolia.
The dusky grasshopper attacks host plants in several ways. Sitting
head-up on a leaf of needleandthread grass, an adult may begin feeding
halfway up the leaf, cut through it, hold onto the cut section with
the front tarsi, and consume it to the dry tip. Occasionally an
adult will turn head-down on a grass or sedge and feed on green
basal tissue. On short host plants such as needleleaf sedge, an
adult from a horizontal position on the ground may reach up with
its mouthparts and begin to feed on a green leaf 3/4 inch above
its base, cut through it, hold onto the cut section, and consume
it as far as the dry tip. From a horizontal position on the ground,
adults may feed on recumbent green leaves or stubs of host plants.
A noteworthy observation was made of the feeding of a nymph (instar
IV) perched head-up on a 4-inch leaf of needleandthread. The nymph
did not feed on the leaf on which it rested but reached out with
its mouthparts and fed on the tip ends of three younger, 2-inch
leaves. Dusky grasshoppers appear to be thrifty feeders as they
consume most of whatever they attack eating all of the green and
dropping chiefly the dry brown parts of leaves. They have been observed,
however, to feed on dry plant litter and on dry cow dung.
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The long wings and strong thoracic muscles of the dusky grasshopper
enable it to disperse and migrate by flight. A significant observation
indicative of migrant behavior was made of a mixed swarm consisting
of seven species that landed in downtown Cheyenne, Wyoming, on 27
September 1993. From a total of 63 collected specimens, three males
and three females of the dusky grasshopper were obtained. The collection
of grasshoppers suggested dispersal from a heavily infested site
of the mixedgrass prairie that surrounds Cheyenne.
Another example of fall dispersal by the dusky grasshopper is that
of a population in western Nebraska that moved from depleted rangeland
into adjacent winter wheat on 27 September 1967. Adults were also
found in winter wheat in southeast Wyoming during October 1992,
indicating earlier dispersal from surrounding mixedgrass prairie.
In flushed flight, the dusky grasshopper softly crepitates and
travels 3 to 9 feet at heights of 3 to 12 inches. The flight is
usually straight, with an occasional turn near the end.
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Figures 1-5. Appearance
of the five nymphal instars, their sizes, structures, and
color patterns. Notice progressive development of wing pads.
BL=body length, FL=Hind Femur Length. AS=number of antennal
First Instar: BL 4.5-4.7 mm FL 2-2.2 mm AS 11-12.
Second Instar: BL 5.2-6.9 mm FL 2.9-3.5 mm AS 13-16.
Third Instar: BL 6.7-8.2 mm FL 4-5.3 mm AS 16-18.
Fourth Instar: BL 10.1-13.7 mm FL 5.5-7.2 mm AS
Fifth Instar: BL 10.7-16 mm FL 7.3-9.3 mm AS 23-25.
Figures 6-10. Appearance
of the adult male and two females, spread wings, egg pod,
and exposed eggs.
Adult Male: BL 15-18.5 mm FL 9.5-11 mm AS 24-25.
Adult Female: BL 21.5-25.5 mm FL 11.5-14 mm AS
Green form of adult
Spread wings of female.
Egg pod and exposed eggs (bottom of pods at right).
The dusky grasshopper is a medium-sized, dark brown, sometimes
greenish species with long wings that extend 1 to 4 mm beyond the
end of the abdomen (Fig. 6-8). The tegmina are banded and the hind
wings have weak apical dark bands. Occasionally these bands are
dark and distinct (Fig. 9). The fastigium is distinctly longer than
wide in males and ranges in females from slightly to distinctly
longer than wide. The outer surface of the hind femur has three
dark bands and the knee is dark. The hind femur of green specimens
may have only weak bands or none at all. The hind tibia is blue.
The nymphs are identifiable by their structures, color patterns,
and shape (Fig. 1-5).
- Head. Face moderately slanting; antennae short and weakly clavate
(club-shaped) in instars I to III, filiform in instars IV and
V, compound eyes brown with pale tan spots, light line runs from
base of antennae diagonally across middle of eye.
- Pronotum with distinct median carina and plainly evident lateral
carinae, disk sloping but not tectate; in green individuals usually
a reddish brown to purple band runs down middle of pronotum and
continues onto mesonotum, metanotum, and abdomen.
- Hind femur with outer medial area green, tan, or grayish brown;
instar I with medial area often pink in distal half. Tibia and
femur of fore- and midlegs carinate (ridged) longitudinally; four
ridges visible on outer face, often with black lines between the
- Body color green, tan, or grayish brown.
The early instars (I to III) of the dusky grasshopper and of
Chortophaga viridifasciata appear similar; both are
usually green and structurally similar. They may be separated by
a few characteristics that differ. The antennae of the dusky grasshopper
are clavate while those of C. viridifasciata are ensiform.
The outer faces of the femur and tibia of the fore- and midlegs
of the dusky grasshopper have four distinct longitudinal ridges,
which usually have black lines between them. Those of C. viridifasciata
have two distinct ridges, which are the upper and lower carina,
and a third weak ridge between them with no black lines between
the ridges. Instar I of the dusky grasshopper has the medial area
of the hind femur pink in the distal half, and that of C. viridifasciata
is entirely green. Instars IV and V are identifiable by the shape
of the pronotum. The disk of the dusky grasshopper slopes moderately,
and that of C. viridifasciata is tectate (steep roof-like);
the posterior angle of the disk in the dusky grasshopper is obtuse,
and that of C. viridifasciata is acute.
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The dusky grasshopper is an intermediate-developing species. In
the northern mixedgrass prairie hatching of eggs begins in early
to mid June, about three weeks after the initial hatch of Ageneotettix
deorum. The hatching period is prolonged, continuing for six
to eight weeks. The unusually long period may be due to early and
late oviposition in the fall and to heterogeneous soil temperatures
in well-vegetated habitats.
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The nymphs develop during early summer when temperatures are warm
and host plants are green. The nymphal period, however, is relatively
long. Based on first appearances of the first instar and the adult
in the northern mixedgrass prairie, this period ranges from 56 to
66 days. Both males and females require five instars to complete
nymphal development. In the species' southern distribution, such
as northeastern Texas, juvenile stages are present throughout the
year and at least two generations occur annually.
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Although dusky grasshoppers may disperse by flight, the majority
of adults remain in the habitat in which the eggs hatched and nymphs
developed. Adults begin to appear August 8 to 10 in the mixedgrass
prairie of southeast Wyoming (altitude 5,200 feet) and August 11
to 14 in the mixedgrass prairie of southwest Saskatchewan (altitude
2,100 feet). In northeastern Texas, adults appear by mid April and
the adults of a second generation by August. Fledgling adults are
sexually immature. They require two to three weeks of growth and
maturation before mating and producing eggs. Oviposition may ensue
by the 16th day of adulthood. An unknown number of days prior to
oviposition, pair formation, courtship, and mating occur. Males
make frequent crepitation flights to arouse the females. When an
individual grasshopper moves nearby, a male on the ground in pursuit
of a mate produces a single burst of vibratory stridulation. Then
the male moves toward the individual while making a single pulse
of ordinary stridulation. If the individual is a receptive conspecific
female, she will lower her hind femur closest to the courting male,
spread it away from her abdomen, and turn her genitalia toward the
courting male as he mounts. During copulation the male transfers
a spermatophore (a proteinaceous capsule enclosing sperm)
to the female.
For oviposition, females select bare ground that is interspersed
among the native grasses of their habitat. Females test the soil
by boring into the ground several times before finally depositing
a clutch of eggs. When given a choice of five Texas soil types,
ranging in coarseness from clay to gravel, ovipositing females preferred
Houston black clay; they laid 111 of 204 egg pods in this soil.
Males often attend an ovipositing female and may contact her, but
they are kicked away by the female. After completing oviposition
and withdrawing her ovipositor from the soil, the female brushes
particles of soil and litter over the aperture of the hole with
her hind tarsi. The pods are 3/4 inch long, slightly curved, and
contain from 14 to 20 eggs (Fig. 10). Eggs are tan and 4.0 to 4.4
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The ecology of the dusky grasshopper has been investigated by several
scientists working at the Matador site of the International Biological
Program (east of Kyle, Saskatchewan). This site supports a minor
type of the northern mixedgrass prairie, characterized by heavy
clay soil and vegetation dominated by northern wheatgrass, western
wheatgrass, and needleleaf sedge.
An assemblage of 19 species of grasshoppers occupied the site during
the period of study from 1967 to 1971. In 1968 the dusky grasshopper
made up approximately 74 percent of the population, reaching a peak
density of 12 early instar nymphs per square yard. Mortality of
young nymphs was high in both 1968 and 1969. Daily mortality decreased
after the grasshoppers reached instar IV. The average daily mortality
from instar IV through the adult stage was 3 percent in 1968 and
5 percent in 1969. The population gradually declined from 1968 to
1971. The unusually luxuriant growth of vegetation in 1970 and 1971
suggested that the cause of grasshopper decline was decreased soil
temperature due to shading of the soil surface. These physical factors
delayed the development and maturation of the dusky grasshopper,
resulting in a decrease of egg production. Additionally, because
the dusky grasshopper oviposits in bare ground, a reduction of such
sites probably incited adults to emigrate. Circumstantial evidence
for such movement was observed after lightning caused a fire in
part of the study area in August 1969. All grasshoppers perished
in the burned area, but the next year dusky grasshoppers migrated
from the unburned area, which supported a heavy growth of vegetation,
to the burned area, which supported light growth and contained an
abundance of bare ground.
Observations in Montana, Texas, and Saskatchewan indicate that
the dusky grasshopper finds a favorable habitat in sites of heavy
clay soil covered by a good growth of wheatgrasses or needlegrass
and prevalent bare ground for basking and oviposition. Nevertheless,
the species also inhabits areas of fine sandy loam soil in the mixedgrass
prairie. As a case in point, in southeast Wyoming (Laramie County),
sites dominated by blue grama, needleandthread, and needleleaf sedge
support assemblages in which the dusky grasshopper is a subdominant
with densities of 0.1 to 1 young adult per square yard. In a few
roadside sites, with sparse western wheatgrass and abundant bare
ground, the dusky grasshopper becomes dominant and reaches peak
densities of approximately ten young adults per square yard.
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The dusky grasshopper is a geophilus species, spending almost all
of its time on the ground. At night it rests sitting horizontally
on bare soil and litter, often resting under a thin canopy of leaves
and surrounded closely by the grasses of its habitat. One to two
hours after sunrise, individuals begin to bask on bare ground by
turning a side perpendicular to the rays of the sun and lowering
the associated hindleg to expose the abdomen. They bask for two
to three hours and then become active - walking, flying occasionally,
and feeding. The males search for mates and may chase after females
on the ground. Nonreceptive females may escape by flight. Feedings
have been observed to occur during midday hours from 9:12 a.m. to
1:27 p.m. DST at ground temperatures ranging from 76°F to 126°F
and air temperatures 66°F to 79°F. At extreme high temperatures,
125°F and higher, the grasshoppers take evasive actions to avoid
overheating. They rest in partial shade or sit on grass one-half
inch above the ground surface. They may crawl into the full shade
of grasses or climb onto litter, thus raising themselves about an
inch above the soil surface. In the latter position they face the
sun exposing the least body surface. When temperatures ameliorate,
the grasshoppers once more become active. On 29 September 1992,
3:40 p.m. DST, in the mixedgrass prairie of southeast Wyoming, an
aggregation of two males and six females was observed underneath
a dry cow dropping that had been hollowed out by their feeding.
Later in the day the grasshoppers bask for a second time until
sunset, after which they enter nighttime shelters.
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Anderson, N.L. and J.C. Wright. 1952. Grasshopper
investigations on Montana range lands. Montana Agr. Exp. Stn. Bull.
Bailey, C.G. and P.W. Riegert. 1971. Food preferences
of the dusky grasshopper, Encoptolophus sordidus costalis (Scudder)
(Orthoptera: Acrididae). Canadian J. Zool. 49: 1271-1274.
Bailey, C.G. and P.W. Riegert. 1973. Energy dynamics
of Encoptolophus sordidus costalis (Scudder) (Orthoptera:
Acrididae) in a grassland ecosystem. Canadian J. Zool 51: 91-100.
Isely, F.B. 1937. Seasonal succession, soil relations,
numbers, and regional distribution of northeastern Texas acridians.
Ecol. Monog. 7: 318-344.
Knutson, H. 1937. A study of Encoptolophus sordidus
costalis (Scudder) in northeastern Texas. M.S. thesis, Southern
Methodist University, Dallas, Texas.
Otte, D. 1970. A comparative study of communicative
behavior in grasshoppers. Misc. Publ. Mus. Zool., Univ. Michigan.
Riegert, P.W. and J.L. Varley. 1972. Above-ground
invertebrates I. Population dynamics. Tech. Rpt. No. 6 Matador Project,
Univ. Saskatchewan, Regina campus, Canada.
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