Melanoplus dawsoni (Scudder)
Wyoming Agricultural Experiment Station Bulletin 912
Species Fact Sheet
by Robert E. Pfadt
Geographic range of Melanoplus
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The Dawson grasshopper is a small short-winged species that ranges
in northern grasslands from the Atlantic coast to the Great Basin
of the West. It is a common grasshopper in the mixedgrass prairie
and in grass-forb parks at high altitudes (7,000 to 8,500 feet). In
Colorado it is a rare resident at 10,000 feet. At lower altitudes
it frequently inhabits the bottoms of ravines where grasses, forbs,
and shrubs grow profusely.
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Some entomologists have concluded that the Dawson grasshopper is
of little economic importance. Nevertheless, observed densities
of 4 to 10 adult grasshoppers per square yard in the northern mixedgrass
prairie indicate a potential for damage, especially to pastures
in this region seeded to legumes.
Alfalfa fields in North Dakota are frequently infested with the
Dawson grasshopper in addition to six other species of Melanoplus,
namely, M. bivittatus, M. femurrubrum, M. sanguinipes,
M. packardii, M. gladstoni, and M. differentialis.
Of 12 counties surveyed in 1958 and 1959, two (Benson and Ramsey)
harbored dominant numbers of the Dawson grasshopper (42 and 67 percent
of the collected grasshoppers, respectively). Of 409 Dawson crops
examined, 344 or 84 percent contained alfalfa fragments equalling
the frequency of alfalfa in the crops of M. femurrubrum,
a recognized serious pest of alfalfa.
Weights of the Dawson grasshopper are similar to weights of the
little spurthroated grasshopper, Melanoplus infantilis. Live
weights of males average 156 mg and females 238 mg (dry weights
males 47 mg, females 73 mg). Weighed within 24 hours after molting
into the adult stage, live weights of males averaged 94 mg and females
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The Dawson grasshopper feeds principally on forbs. Forty species
of forbs belonging to 13 plant families are known to be ingested.
Two families, the bean and sunflower, appear to include the known
principal host plants: western ragweed, leadplant, and milkvetches.
Additionally, two introduced plants, both legumes, alfalfa and white
clover, are among its host plants. White clover has become an important
host plant due to its widespread invasion of pastures, foothill
rangelands, mountain meadows, and roadsides. In cage tests the Dawson
grasshopper has shown a marked preference for dandelion, an introduced
weed that occurs in many of its habitats.
Fragments of 10 species of grasses, usually in small amounts, have
been detected in the crops of this grasshopper. In the sand prairie
of southeast North Dakota, Kentucky bluegrass besides three preferred
forbs (leadplant, western ragweed, and wild rose) appeared to be
consumed in substantial amounts. In a small overgrazed pasture that
lies in a creek bottom in Johnson County, Wyoming, crops of adults
collected late in the season (20 September 1994) contained chiefly
fragments of grass seeds and brome leaves. In a foothill habitat
of the Big Horn Mountains lying at an altitude of 7,190 feet, Dawson
grasshoppers fed upon white clover, 43 percent; Astragalus
sp., 25 percent; golden aster, 16 percent; common yarrow, 5 percent;
grass seeds, 5 percent; and arthropods, 6 percent; as measured by
analyses of crop contents.
Two observations were made of the Dawson grasshopper's method of
attacking a host plant. A nymph (instar V) was observed walking
on the ground in a searching mode. When it came across a sprouting
1-inch forb, it consumed it from tip to base. A female sitting diagonally
head-up, 11 inches high, on a secondary stem of thistle (Cirsium
sp.) crawled 2 inches to a leaf and began to feed on the edge. She
fed for one minute until she was disturbed by the observer. This
meager evidence suggests that the Dawson grasshopper feeds both
by searching the ground and by attacking the leaves of a host plant
close to where an individual may be resting or basking.
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The wide geographic range of the Dawson grasshopper suggests that
the species has both a long evolutionary history in North America
and effective powers of dispersal. Although the majority of adults
are short-winged, a few possess long wings. In a Colorado study,
three of 952 adults (0.3 percent) collected in 14 study sites were
long-winged. A specially relevant observation in this study was
the discovery of one long-winged female at 12,200 feet indicating
a flight distance of approximately 14 miles from the closest resident
population. In 1995, three of 108 (2.8 percent) adults from six
survey sites in Sheridan County, Wyoming possessed long wings.
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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 4.5-5.1 mm FL 2-2.4 mm AS 13-14.
Second Instar: BL 5-6.9 mm FL 2.8-3.4 mm AS 17-18.
Third Instar: BL 6.9-8.8 mm FL 4.3-4.4 mm AS 19-20.
Fourth Instar: BL 8.7-12.5 mm FL 5.3-7.4 mm AS
Fifth Instar: BL 10-13 mm
FL 7.3-8 mm AS 22-24.
Figures 6-10. Appearance
of the adult male and female, hindleg, cercus, and egg pod.
Adult Male: BL 14.5-18.8 mm FL 8.7-9.5 mm AS
Adult Female: BL 17-22.5
mm FL 10-10.8 mm AS 23-25.
Outer face of left hindleg of female.
End of male abdomen showing the cercus
Egg pod and exposed eggs.
The Dawson grasshopper is a small, short-winged species. A small
proportion of the population, however, may possess long wings that
extend 2 to 4 mm beyond the end of the abdomen. Adults are easily
recognized by their small size, short wings, black and yellow ringed
abdominal terga, canary yellow venter, and red hind tibia (Fig 6
and 7). The male cercus is short, slightly concave near the end,
and rounded apically (Fig. 9).
The nymphs are identifiable by their color patterns, shape, and
external structures (Fig. 1-5).
- Head all black except conspicuous yellow band below compound
eye and a median yellow line or band on top. Compound
eye is all black seen without magnification, but under magnification
several scattered light spots are visible.
- Pronotum mainly black; the yellow band below compound eye continues
onto lateral lobe to form a conspicuous crescent; a large black
band is centrally located on the lateral lobe; posteriorly below
it is a yellow triangular marking; a median yellow line or band
is present on the disk. The dorsal stripe of the hind femur is
broad and continuous, a small dorsal yellow wedge in the middle
of the stripe is sometimes present (Fig. 5). The tibia is tan.
- Sides of abdomen are mainly fuscous or gray; in instars I and
II the venter is tan; in instars III, IV, and V it is yellow;
top of abdomen with median yellow band.
- Body colors of black and yellow are shiny and appear polished.
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The Dawson grasshopper begins to hatch about one week after the
migratory grasshopper, Melanoplus sanguinipes. Both belong
to the intermediate-developing group of grasshoppers. In 1979 in
northern Wyoming at an altitude of 3,700 feet, hatching of the Dawson
grasshopper began the first week of June and continued until the
first week of July. At higher altitudes in this region, hatching
occurred later (e.g. at 4,100 feet hatching began on 19 June 1979).
The effect of altitude on the life cycle of the Dawson grasshopper
has been demonstrated nicely in a Colorado study. The study confirmed
the applicability of Hopkin's bioclimatic law. The law, with reference
to altitude in temperate North America, states that for every rise
of 400 feet, events in the life cycle are delayed four days.
The start of hatching at a particular site depends on seasonal
temperatures and precipitation and may vary from one year to another
by as much as four weeks. The hatching period (duration) also varies,
ranging from two to six weeks.
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Both male and female nymphs require five instars to reach adulthood.
Calculations of available data (days from first instars to first
adults) indicate that at high altitudes the nymphal period is shorter
than at low altitudes. For example, in northcentral Colorado nymphal
development lasted 32 days at 5,750 feet, 28 days at 6,700 feet,
and 20 days at 8,500 feet. In northern Wyoming, at 3,700 feet, the
nymphal period lasted 45 days.
Reared in the laboratory at six different temperatures, the Dawson
grasshopper developed at six different rates with nymphal periods
ranging from 21 to 66 days. Up to a point, the higher the temperature
the faster the growth. The highest-rearing temperature of 104°F,
however, retarded development and increased mortality. Of the temperatures
used in these tests, 95°F appeared most favorable, as the nymphs
both developed fastest and survived in greatest numbers.
These experimental results suggest that temperatures in the habitat
have a considerable influence on the rate of development and survival
of this grasshopper. They do not explain, however, shorter life
cycles at higher altitudes where temperatures are cooler. A hypothesis
for variation in length of life cycles of the Dawson grasshopper
living at different altitudes draws on one proposed to explain similar
variation in populations of the migratory grasshopper, Melanoplus
sanguinipes. Resident populations of a species may be genetically
isolated, such that they adapt physiologically to the length of
the growing seasons and other environmental exigencies of their
habitat and pass on these adaptive characters to succeeding generations.
Additionally, grasshoppers at high altitudes make behavioral adjustments
that may equalize heat accumulation of individuals. They bask longer
in the sun and remain longer in their thermal shelters under grass
canopies, litter, and dry cow dung. Because of these responses,
the most important physiological adaptations that grasshoppers at
high altitudes make are to the shorter seasons.
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First appearance of adults occurs from early to late July, with
the precise time depending on seasonal temperatures and altitude.
Transformation to the adult stage continues for four to five weeks;
in mid to late August, only adults are present. The population then
consists of adults of widely different ages. Maturation of adults
has not been studied; however, courtship and copulating pairs have
been observed. A male in search of a mate produces bursts of vibratory
stridulation, and when close to a female he makes a sudden jump
onto her back. He continues to produce bursts of vibratory stridulation
as he attempts to engage her genitalia. If she is receptive, he
succeeds in mating and the two remain in copulo for an undetermined
period. Evidently copulation begins in the morning, as two pairs
observed in a foothill habitat on 19 August 1994, were in copulo
at 9:27 a.m. and at 11:41 a.m. DST.
One attempt at oviposition was observed on 5 August 1994 in a weedy
grass-forb habitat. The female sitting horizontally on litter began
to bore into the ground at 9 a.m. but withdrew her ovipositor five
minutes later. She crawled 6 inches away and began to bore again
into the ground at 9:06 a.m., but again withdrew her abdomen and
crawled away into thick vegetation and became lost to view. Caged
females readily oviposit into bare soil, but they often bore several
times before finally depositing eggs.
Adults are present in habitats at low altitudes (3,500 to 6,000
feet) from mid-July to mid-October, a period of approximately 13
weeks. As long as the supply and condition of host plants persist,
this extended presence of adults gives the species considerable
time to reproduce. At higher altitudes (8,500 feet), the length
of the adult period is shorter, but the species apparently reproduces
as well in resident populations. Rapid development of nymphs at
high altitudes has been documented and accelerated rates probably
include maturation and egg production as well.
The egg pods are 3/4 inch long and slightly curved just above the
eggs. In the region of the eggs, the pod has a diameter of 1/8 inch.
The eggs occupy the lower 1/4 to 3/8 inch of the pod, with pale
yellow or white froth comprising the top part. Pods contain
8 to 14 (average 10.8) tannish yellow eggs that measure 3.6 to 4.5
mm long (Fig. 10).
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Populations of the Dawson grasshopper enjoy the greatest frequency
of occurrence and the highest densities in the northern part of
their geographic range and at high altitudes in the south. The species
occurs commonly in the northern mixedgrass prairie of the Canadian
prairie provinces where populations may increase to 10 adults per
square yard. It is occasionally the dominant species in an assemblage,
but more often it is subdominant to Melanoplus infantilis,
M. sanguinipes, M. packardii, or Encoptolophus
Results of grasshopper surveys in Montana and Wyoming show the
influence of latitude on frequency of occurrence. The Dawson grasshopper
was found in 9 of 55 sites (16 percent) in Montana, but only in
30 of 699 sites (4 percent) in Wyoming.
An important factor in fostering populations of the Dawson grasshopper
appears to be quality and supply of host plants.
The species frequently inhabits abandoned fields and roadsides
where dandelion, volunteer legumes, and other forbs grow abundantly.
In Montana this grasshopper occupied 4 of 11 abandoned fields (36
A study of grasshopper ecology in the northern mixedgrass prairie
of southwest Saskatchewan has shown that when environmental conditions
become favorable for the Dawson grasshopper, populations can increase
seven-fold over a period of four years. The densities during these
years were low: 0.25 per square yard in 1968, 0.4 in 1969, 0.9 in
1970, and 1.7 in 1971.
In the south, favorable habitats of the Dawson grasshopper occur
at high altitudes of 7,000 to 8,500 feet. An example of such a habitat
was discovered in 1994 in the western foothills of the Big Horn
Mountains, Washakie County, Wyoming. Located at an altitude of 7,200
feet, this grassland site was invaded by white clover that served
as the grasshoppers' chief host plant. The density of all species
in an assemblage of mainly young adults sampled on 19 August 1994
was estimated to be 16.5 grasshoppers per square yard. The Dawson
grasshopper was the dominant species with 6.5 individuals per square
The assemblage consisted of four other species: Melanoplus sanguinipes,
5 per square yard; Camnula pellucida, 3.5; M. femurrubrum,
1; and M. infantilis, 0.5. In Colorado, the Dawson grasshopper
is a rare resident at 10,000 feet. Above this altitude the species
is apparently unable to exist. Small populations of the Dawson grasshopper
inhabit the sand prairie (altitude 1,075 feet) of southeast North
Dakota. A 10-year study revealed low densities every season.
In its southern distribution, the Dawson grasshopper often inhabits
the bottom of ravines from where, in outbreak years, they may disperse
to surrounding mixedgrass prairie. When these large populations
crash, the species disappears from the surrounding prairie but persists
in the ravines.
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The Dawson grasshopper is a geophilus species living most of its
life on the ground. In high-altitude habitats where soil and air
temperatures fall below 50°F during the night, individuals rest
in nocturnal shelters. One-half to one hour after the sun strikes
the ground, they emerge from these shelters and begin to bask. Basking
horizontally on the ground, they turn a side perpendicular to the
sun's rays and lower the associated hindleg to expose the abdomen.
The opposite hindleg is held in the normal position with the knee
a few millimeters above the tegmen. They may also bask high on forbs,
turning a side or their back to the sun. They bask for up to three
hours until 10 a.m. DST. Some adults may become active before others
have finished basking. Feeding has been observed as early as 9:30
a.m., courting 9:45 a.m., mating 9:27 a.m., and ovipositional probing
8:41 a.m. During the activity period many may just rest quietly
occasionally stirring and preening. They sit on vegetation or horizontally
on ground litter and usually face away from the sun.
All activity ceases if soil and air temperatures become too hot
for the grasshoppers. Response of adults to soil surface temperature
of 135°F and air 100°F was observed in a low-altitude (4,700 feet)
habitat near Buffalo, Wyoming. The grasshoppers climbed forbs and
grasses and rested vertically, head-up on the shady side of the
plant at heights of 5 to 18 inches. The response of three adults
flushed to the ground was observed. A female jumped 3 feet, landed
on the ground, but almost immediately climbed up 15 inches on the
stem of a wild licorice plant. A male jumped to the ground and after
a few seconds crawled to a nearby grass plant and climbed up the
stem. Another flushed male jumped onto a grass stem and landed 2
inches above ground and in the sun; after several seconds it moved
to the stem of a slimflower scurfpea on which the grass leaned,
crawled to a height of 5 inches, and came to rest vertically head-up
on the shady side of the scurfpea.
When temperatures decline, a second period of activity occurs.
As temperatures fall still further in late afternoon, the grasshoppers
bask for a second time. Finally, just before sunset, they retreat
to shelters. They have been observed to crawl into thick clumps
of grasses and under dry cow dung. In the morning before sunrise,
they have been discovered resting both horizontally on the ground
and upside down on the underside of rocks or dry cow dung, often
along with individuals of other species such as Melanoplus sanguinipes
and Camnula pellucida.
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Alexander, G. and J.R. Hilliard, Jr. 1969. Altitudinal
and seasonal distribution of Orthoptera in the Rocky Mountains of
Northern Colorado. Ecol. Monogr. 39: 385-431.
Anderson, N.L. 1973. The vegetation of rangeland
sites associated with some grasshopper studies in Montana. Montana
Agr. Exp. Stn. Bull. 668.
Mulkern, G.B. 1980. Population fluctuations and
competitive relationships of grasshopper species (Orthoptera: Acrididae).
Trans. Amer. Entomol. Soc. 106: 1-41.
Mulkern, G.B., K.P. Pruess, H. Knutson, A.F. Hagen,
J.B. Campbell, and J.D. Lambley. 1969. Food habits and preferences
of grassland grasshoppers of the North Central Great Plains. North
Dakota Agr. Exp. Stn. Bull. 481.
Riegert, P.W. 1986. The effect of perturbation
on the stability and diversity of grasshopper species on the North
American prairies. Pan Amer. Acridol. Soc. Proceedings 4th Triennial
Meeting, pp. 111-120.
Shotwell, R.L. 1941. Life histories and habits
of some grasshoppers of economic importance on the Great Plains.
USDA Tech. Bull. 774.
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