Clubhorned Grasshopper
Aeropedellus clavatus (Thomas)
Link directly to photos of adults, nymphs,
or eggs.
Distribution and Habitat
A. clavatus continental distribution map
Wyoming distribution map
The clubhorned grasshopper, Aeropedellus clavatus (Thomas), inhabits
grasslands of western Canada and the northern United States and extends
its range into mountainous areas as far south as Arizona and New Mexico.
In Colorado, one resident population survives above timberline at 13,600
feet in a rocky, grass-sedge habitat. In the prairie provinces of Canada
it is the most widely distributed and abundant of the grassland species,
occurring on all dry and somewhat sandy areas south of the boreal forest.
In four of ten years it was the dominant species of a grasshopper assemblage
inhabiting the sand prairie of southeastern North Dakota.
Economic Importance
The clubhorned grasshopper is primarily a pest of grasses and sedges in
the mixedgrass and bunchgrass prairies and in mountain meadows and parks.
Populations may reach 20 per square yard on rangeland in Canada, causing
severe damage to forage grasses. It has also attacked seedling cereals;
in 1936 an outbreak in Saskatchewan destroyed 300 acres of wheat. In Montana
and North Dakota it is frequently abundant in grasshopper assemblages infesting
rangeland.
Food Habits
The clubhorned grasshopper feeds on grasses and sedges. Examinations of
crop contents show that in mixedgrass prairie this grasshopper feeds on
western wheatgrass, prairie junegrass, Sandberg bluegrass, needleandthread,
threadleaf sedge, and needleleaf sedge. In mountain meadows and parks different
groups of grasses and sedges are used for food. Wherever Kentucky bluegrass
has invaded an area, it is a preferred host plant. When grass seeds and
glumes become available in the habitat, they are fed upon heavily. The
clubhorned grasshopper is known to feed upon 28 species of grasses and
six species of sedges. Small amounts of forbs, fungi, pollen, and arthropod
parts have been found in crop contents.
Migratory Habits
Little is known about the migratory habits of the clubhorned grasshopper.
The females do not fly; their wings are short, not reaching the middle
of the abdomen. Males have either short or long wings. In plains habitats
the long-winged males fly extensively. A study of predator avoidance conducted
above timberline in Colorado showed that the females merely hop away from
a predator but the males hop away and then prance (i.e., they take small,
repeated hops without appreciable progression).
Identification
Adults of the clubhorned grasshopper are medium-sized and colored gray
or green with various markings (Fig. 5
and Fig. 6). They possess clavate
antennae that give this grasshopper both its common name and scientific
species name. The six terminal segments of an antenna are enlarged and
dark. The head has a dark streak running from beneath the compound eye
to the base of mandible. Anterior to this streak lies a vertical cream
or light tan band. The head has distinct oblong lateral foveolae (Fig.
7). The pronotum has low but definite median carina and lateral carinae,
all of which are cut once by a sulcus behind the middle; the lateral carinae
converge (curve inward) near the middle of the prozona (Fig.
7); the lateral lobe usually bears a pale diagonal mark (Fig.
6).
The nymphs are identifiable by their shape, external structures, and
color patterns (Fig. 1-4):
1. Head with strongly slanted face; antennae flat and nearly same width
the entire length in females, clavate in males (instars II to IV); lateral
foveolae oblong and distinct.
2. Narrow light line beginning behind middle of compound eye, running
along side of head onto lateral carina of pronotum and continuing on abdomen;
broad fuscous stripe adjacent and below the light line.
3. Pronotum with lateral carinae converging near middle.
4. Hind femur with entire medial area gray; lower marginal area pale
gray.
Hatching
The clubhorned grasshopper is a very early-hatching species. Nymphs begin
to emerge ten days before nymphs of the bigheaded grasshopper, or about
the first week in May in eastern Wyoming. The hatching period lasts for
three to four weeks. In mountain areas above timberline in Colorado, hatching
begins in mid to late June depending on altitude, location, and seasonal
temperatures.
Nymphal Development
The clubhorned grasshopper has four instars that develop rapidly. Accelerated
development is a life history adaptation frequently associated with boreal
existence. Nymphal development is completed in approximately 30 days on
the plains and 42 days in alpine habitats.
Adults and Reproduction
The adults remain in the same area in which the eggs hatch and the nymphs
develop. Because of early hatching and rapid development, the adults emerge
when there is still an abundance of green grasses and sedges available
for food. However, the cost of this early access to food is that this grasshopper
may be intensively controlled by predators. Birds, rodents, spiders, and
predaceous insects usually reduce the number of clubhorned grasshoppers
to fewer than one per square yard by early summer. Later-hatching species,
such as the bigheaded and whitewhiskered grasshoppers, may numerically
overwhelm predators (trading more intensive competition over poorer food
for the potential of swamping the predators' response) and thereby remain
abundant through early summer.
Courtship and fecundity have not been studied in this grasshopper. The
males stridulate loudly by vibrating the hind femur through a small arc
against a raised vein on the tegmen. The "song" is probably part of the
courtship ritual. Females select grasses or sedges in which to oviposit,
laying the eggs among the roots. The eggs develop rapidly to stage 26 in
which the embryo appears as a young grasshopper nearly ready to hatch.
Evidently the embryo has entered diapause, as it does not emerge until
the following spring. Egg pods (Fig. 8)
are 10 to 13 mm long and 3.5 to 4.0 mm in diameter; they are oriented vertically
in the soil. The pods contain five to eight eggs surrounded by a tan, hardened
froth. Eggs are light tan and 4.6 to 5.5 mm long. They are arranged in
two rows and are inclined about 30 degrees from vertical.
The species has one generation annually in plains habitats. The eggs
of resident populations of alpine habitats pass through two, or possibly
three, winters before hatching.
Population Ecology
Outbreaks of the clubhorned grasshopper occur in limited areas of the prairie
provinces of Canada, where populations may increase to 20 per square yard.
In at least one instance, this grasshopper was abundant in a year that
followed an unusually wet year. In relatively lush habitats of the mixedgrass
prairie in Wyoming, populations may increase to four adults per square
yard in early summer. More often, the densities in these habitats range
from one to two adults per square yard.
Daily Activity
Cursory observations of adult activity have been made in Montana. Males
appear to do much crawling on the ground and they frequently take short
flights. The females are slower and remain motionless on the ground for
long periods. Further observations of their daily activities are desirable.
Selected References
Alexander, G. and J.R. Hilliard, Jr. 1964. Life history of Aeropedellus
clavatus (Orthoptera: Acrididae) in the alpine tundra of Colorado. Ann.
Entomol. Soc. Am. 57: 310-317.
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. Bull. 486.
Beirne, B.P. 1972. Pest Insects of annual crop plants in Canada. IV.
Hemiptera-Homoptera V. Orthoptera VI. Other groups. Mem. Entomol. Soc.
Canada No. 85.
Kevan, P.G., J.G.H. Cant, D.K. McE. Kevan. 1983. Predator avoidance
posturing of grasshoppers (Orthoptera: Acrididae) from the Colorado alpine
and plains. Can. Entomol. 115: 115-122.
Mulkern, G.B. 1980. Population fluctuations and competitive relationships
of grasshopper species (Orthoptera: Acrididae). Trans. Am. Entomol. Soc.
106: 1-41.
Ueckert, D.N. 1968. Seasonal dry weight composition in grasshopper diets
on Colorado herbland. Ann. Entomol. Soc. Am. 61: 1539-1544.
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