Metator pardalinus (Saussure)
Wyoming Agricultural Experiment Station Bulletin 912
Species Fact Sheet
by Robert E. Pfadt
Geographic range of Metator
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The bluelegged grasshopper, a large bandwinged species, has a wide
geographic range in western North America. It inhabits the shortgrass,
mixedgrass, bunchgrass, desert, and tallgrass prairies. In the northern
mixedgrass prairie, where populations reach their highest densities,
the species prefers to live in areas dominated by western wheatgrass.
These are mesic habitats commonly occurring on clay soil flats, in
valley bottoms, and in old dry lake beds. The close plant-insect relationship
is probably the main reason for a patchy distribution of this grasshopper.
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The bluelegged grasshopper is a heavy feeder on native grasses,
particularly western wheatgrass, which abounds in its preferred
habitats. Calculations made from a quantitative study of damage
in Montana indicate that a density of one bluelegged grasshopper
per square yard causes a loss of approximately 100 pounds (air-dry
weight) of grass per acre. This figure appears unusually high, suggesting
the need for further study of damage by this grasshopper.
The damage is usually done in participation with other rangeland
species, often with the bigheaded grasshopper, Aulocara elliotti,
or the whitecrossed grasshopper, Aulocara femoratum. The
densities of the bluelegged grasshopper in assemblages occupying
its preferred habitats usually range from one to four adults per
square yard, but in some situations densities may reach ten per
The bluelegged grasshopper is a large species. Live weights of
males from northern mixedgrass prairie average 294 mg and of females
828 mg (dry weights: males 97 mg, females 236 mg).
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The bluelegged grasshopper feeds almost exclusively on grasses
and sedges. It has been observed to feed on the green leaves of
western wheatgrass, bluebunch wheatgrass, needleandthread, green
needlegrass, sand dropseed, prairie junegrass, and blue grama. Microscopic
examination of crop contents of late instars (IV and V) and adult
males collected from a western wheatgrass habitat in the northern
mixedgrass prairie of eastern Wyoming revealed that these grasshoppers
were ingesting two host plants exclusively - western wheatgrass
and needleleaf sedge in nearly equal amounts. In a Nebraska study,
crops of two specimens from a site near Scottsbluff contained solely
prairie sandreed fragments. The bluelegged grasshopper also feeds
on both green and dry grass litter and on dry cattle droppings.
Although this habit suggests the species should eat bran bait, insecticidal
tests indicate otherwise, as only a 2 percent reduction was achieved
in a population treated with carbaryl bran bait. Adults have been
observed feeding ravenously on a small matforming lichen. This behavior
sometimes gives the appearance that the grasshoppers are eating
The method of attacking a host plant by this grasshopper is unusual.
Crawling on the ground, a hungry adult contacts a host plant such
as western wheatgrass or needleandthread, climbs the plant, and
cuts a 3 to 4 inch terminal section of leaf, which falls to the
ground. The grasshopper immediately drops to the ground and recovers
the cut section. Handling the cut terminal with its front tarsi,
the grasshopper devours it from one end to the other. While searching
for food, a hungry grasshopper may instead contact a green section
of leaf lying on the ground or an attached recumbent leaf and feed
on it. The method of attack used by instars II to V is similar to
the adults; they climb and cut terminal sections of leaves and feed
on them from a horizontal position on the ground or they feed on
ground litter, both green and dry grass leaves. No observations
of feeding of instar I have been made.
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Possessing long wings that extend beyond the end of the abdomen
and strong powers of flight, the bluelegged grasshopper is well
known for its vagrant tendencies. In Colorado its upper resident
altitude is 5,800 feet at the western edge of the plains, but adult
"accidentals" have been collected farther west at several
locations in the mountains, the highest at 11,400 feet.
Evasive flights begin about 8:30 a.m. DST on clear days when soil
temperatures have risen above 60°F. These flights are straight and
6 to 12 inches high, the adults softly crepitating and travelling
distances of 3 to 15 feet.
Although no direct observations of group migratory flights have
been made, circumstantial evidence indicates that such behavior
occurs. In eastern Wyoming a preferred habitat dominated by western
wheatgrass became drought stricken in July 1989, and the usually
luxuriant grasses stopped growing and turned brown. Where
both the bigheaded grasshopper and the bluelegged grasshopper occurred
in economic densities on 1 July 1989, only the bigheaded grasshopper
remained at high densities 20 July 1989. The bluelegged grasshopper
had disappeared and presumably emigrated to more favorable habitats
that had received spotty rainfall during the summer. Two possible
stimuli for the emigration of the bluelegged grasshopper were the
exhaustion of its preferred food plants and the deterioration of
the microhabitat. On the other hand, the bigheaded grasshopper,
with less stringent ecological requirements, chose to remain in
the deteriorating habitat.
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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 5.9-7.6 mm FL 3.5-3.7 mm AS 9-10.
Second Instar: BL 7.4-9.3 mm FL 4.5-5 mm AS 11-14.
Third Instar: BL 9.5-11.9 mm FL 5.8-6.2 mm AS
Fourth Instar: BL 10.9-15 mm FL 6.4-9.3 mm AS 17-18.
Fifth Instar: BL 12.5-20 mm FL 8.4-11.9 mm AS 19-20.
Figures 6-10. Appearance
of the adult male and female, the hindleg, spread wing, and
Adult Male: BL 22-25 mm FL 13.5-14.5 mm AS
Adult Female: BL 30-34 mm FL 15.2-18 mm AS 21-13.
Spread wings from left side.
Inner face of female hindleg.
Loose eggs from single pod.
The bluelegged grasshopper is a large, tan and brown grassland
species (Fig. 6 and 7). The posteroventral angle of the pronotal
lobe is acute and drawn down. The tegmen has numerous dark brown
spots and a pale streak on the outer edge of the dorsal field. The
streaks of the folded tegmina converge posteriorly. The hindwings
are marked by a wide outer dark band and the inner or basal area
is colored yellow, orange, or red (Fig. 8). The inner face of the
hind femur has alternating bands of light and dark blue; the band
next to the knee is sometimes tan (Fig. 9). The hind tibia of the
male is medium blue, that of the female is light blue on the outer
face and medium blue on the inner face. The male often has top and
sides of the abdomen (the terga) colored blue.
The nymphs are identifiable by their shape, structures, and color
patterns (Fig. 1-5).
- Head: face nearly vertical, a diagnostic light band beginning
from near top of compound eye and running diagonally backwards
on the occiput, the band from one eye converges on the other but
the bands do not meet, bands sometimes faint. Figures 1-5 show
side view of left band beginning above compound eye and running
diagonally on occiput.
- Pronotum with disk wrinkled; median carina distinct and elevated
higher on the prozona than the metazona, cut twice, in front of
middle and near middle; lateral lobe with posteroventral angle
acute and drawn downward.
- Hind femur with sparse hairs on lower carina; this characteristic
separates bluelegged nymphs from Kiowa grasshopper nymphs (Trachyrhachys
kiowa), which possess a thick fringe of hairs on the lower
carina. Color of hind tibia of instars I and II is fuscous, of
instars III and IV fuscous and gray, of instar V pale blue or
pale blue, tan, and fuscous.
- General body color tan to brown with many dark brown maculations
imparting a dark brown aspect to all instars.
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Eggs of the bluelegged grasshopper hatch two to three weeks after
those of the bigheaded grasshopper, placing the former species in
the intermediate-hatching group. Although egg development of the
bluelegged grasshopper has yet to be investigated, we may speculate
from its seasonal development and from the results of studies of
other rangeland species that the embryos begin to develop in summer,
shortly after the eggs are laid, and continue developing until they
diapause in an undetermined embryonic stage in fall. Sheltered in
soil cells at depths of 1 to 2 inches, the eggs pass the winter
and then complete development the following spring. We postulate
that eggs of the bluelegged grasshopper diapause in approximately
the same developmental stage as eggs of the bigheaded grasshopper,
but because of greater depth in the soil eggs of the former species
take longer to accumulate the required heat units for completion
of their embryonic development and hatching.
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In the northern mixedgrass prairie, nymphs emerge in June over
a short period, possibly as short as one week. They feed and develop
in the same habitat as they hatch and dwell on the ground surface.
Their nymphal development consists of five instars and takes about
36 days to complete.
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Adults of the bluelegged grasshopper may disperse to new areas,
but the majority remain in the same favorable habitat in which the
nymphs hatched and developed. There they feed, mature, reproduce,
and eventually are eaten by a predator or die from other causes.
Observations have not been made of the courting and mating behavior
of this grasshopper, but several observations of oviposition in
northern mixedgrass prairie have been made. A gravid female ready
to lay selects either bare ground or ground covered by litter among
shortgrass, if available, and works her ovipositor 2 inches deep
into the soil. The time taken to begin and end oviposition has not
been observed, but one female with her ovipositor already inserted
took 32 minutes until withdrawal. A female covers the hole by tamping
with her hindlegs and brushing with her ovipositor. A clutch consists
of 14 large reddish brown eggs measuring 6.3 to 7.3 mm in length
(Fig. 10). There is one generation annually.
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Populations of the bluelegged grasshopper reach their highest densities
in habitats dominated by western wheatgrass. These habitats commonly
occur under mesic conditions, as in dry lake basins (playas), valley
bottoms, and on clay soil flats. In especially favorable habitats,
populations may reach a peak density of ten adults per square yard,
but usually densities are much less. In a 15 acre playa in the northern
mixedgrass prairie of eastern Wyoming, where from 1981 to 1985 adults
of the bigheaded grasshopper ranked first in abundance (adult densities
of 18, 26, 17, 14, and 9 per square yard in the successive years),
the bluelegged grasshopper ranked second (1.7, 1.1, 1.8, 1.8, and
2.8 per square yard). Populations of both species were still high
in the spring of 1989, but a severe summer drought caused the vegetation
to desiccate and the adults of the bluelegged grasshopper to emigrate.
Thus, the bluelegged grasshopper appeared to be more sensitive to
conditions of the vegetation and to moisture than the bigheaded
grasshopper. Under favorable moisture conditions populations of
both species remained high but did fluctuate. The rises and falls
of the populations of the two species were not synchronous. In given
years the population of one species increased while the other decreased.
A biological control factor affecting populations of the bluelegged
grasshopper is parasitism by the tangleveined fly, Trichopsidea
clausa. In some years 80 percent of females in a population
are infested with parasitic larvae. A parasitized female is unable
to reproduce, as all eggs and soft tissues are consumed by an invading
larva. Upon developing to maturity a larva leaves its host, which
then dies. Interestingly, the bigheaded grasshopper is not affected
by this parasite. The tiny larva, 0.5 mm in length, may invade an
individual but it is sealed off and killed by the resistant host.
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The bluelegged grasshopper is a ground-dwelling insect. Both nymphs
and adults sit horizontally on the ground through the night. Many
take positions on ground litter among grasses or on bare ground
under canopies of grasses. Others may just sit on bare ground unprotected
and exposed to the chilling night temperatures. At sunrise the grasshoppers
are found facing in various directions. About two hours later they
begin to bask by exposing a side perpendicular to the rays of the
sun and lowering the hindleg of the exposed side to the ground.
They may also lower both hindlegs to the ground while basking. In
both postures the hindlegs are flexed. Some may bask for as long
as three hours until 10:30 a.m. (DST), but normal activities of
feeding, walking and seeking a mate usually begin about 10 a.m.,
when ground temperature reaches approximately 80°F and air temperature
reaches 67°F 1 inch high above ground.
In the afternoon, activity ceases when temperatures of the soil
surface rise to 120°F. The nymphs may rest horizontally on the ground
in shade of vegetation or may climb on grasses to a height of 2
inches. Adults may rest horizontally on the ground in the shade
of vegetation or they may move into the crowns of grasses and rest
diagonally on leaf stems in the shade. Later, when temperatures
decline the grasshoppers become active again and begin normal activities.
In the evening they bask in the waning rays of the sun and eventually
select their night-time locations.
Observations of the species in Montana have revealed that older
nymphs and the adults are gregarious. Older nymphs were found in
small aggregations while the adults were found in large aggregations.
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Alexander, G. 1964. Occurrence of grasshoppers
as accidentals in the Rocky Mountains of northern Colorado. Ecology
Anderson, N. L. 1973. The vegetation of rangeland
sites associated with some grasshopper studies in Montana. Montana
Agr. Exp. Stn. Bull. 668.
Anderson, N. L. and J. C. Wright. 1952. Grasshopper
investigations on Montana range lands. Montana Agr. Exp. Stn. Tech.
Onsager, J. A. and G. B. Mulkern. 1963. Identification
of eggs and egg-pods of North Dakota grasshoppers. North Dakota
Agr. Exp. Stn. Bull. 446 (Tech.).
Otte, D. 1984. The North American Grasshoppers,
Vol. II Acrididae, Oedipodinae. Harvard University Press: Cambridge,
Pooler, P. D. 1989. Factors influencing grasshopper
oviposition site selection on South Dakota rangelands. M.S. thesis,
South Dakota State University, Brookings, SD.
York, G. T. and H. W. Prescott. 1952. Nemestrinid
parasites of grasshoppers. J. Econ. Entomol. 45: 5-10.
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