Four-spotted grasshopper (Phlibostroma quadrimaculatum)

Phlibostroma quadrimaculatum Four-spotted grasshopper
Distribution
Alberta, Saskatchewan, Manitoba, Idaho, Montana, Wyoming, Utah, Colorado, Arizona, New Mexico, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Texas, Minnesota, Iowa
Taxonomy
Family:	Acrididae
Subfamily:	Gomphocerinae
Genus:	Phlibostroma
Additional resources
Full taxonomy at OSF

The four-spotted grasshopper (Phlibostroma quadrimaculatum) is a common medium-sized, ground-dwelling, grassland species found primarily in dry grasslands and prairies of the central and southwestern United States. It is named for the four distinct dark spots typically visible on its hind wings during flight. These grasshoppers are occasionally a rangeland pest during outbreaks along with other species.

Nomenclature

Phlibostroma quadrimaculatum (Thomas, 1871). For full nomenclature, see this taxon's page on Orthoptera Species File

Identification

Phlibostroma quadrimaculatum is a species of slant-faced grasshopper in the family Acrididae. Slant-faced grasshoppers are recognized by their angled facial profile and typically slender, streamlined bodies with forward-tipped, pointed heads. Most slant-faced grasshoppers in North America belong to the subfamily Gomphocerinae, commonly known as “stridulating slant-faced grasshoppers” or “tooth-legged grasshoppers,” named for the row of pegs on the inner hind legs of males used to produce sound by rubbing against the wing edges. A smaller group with similar facial structure—the Acridinae, or “silent slant-faced grasshoppers”—lacks these pegs and does not produce sound. These silent forms are found in some parts of the United States but are absent from western Canadian grasslands.

The four-spotted grasshopper belongs to Gomphocerinae. Members of this subfamily can be readily distinguished from other grasshopper groups: they lack the prosternal spine found in Melanoplinae and the large, colorful, lobed hind wings typical of Oedipodinae. They also differ behaviorally and morphologically from Acridinae.

A few specialized anatomical terms are useful for identifying grasshoppers in this subfamily. Grasshoppers have four wings, with the leathery, protective front pair known as the tegmina. Just behind the head lies the pronotum, a saddle-shaped structure forming the upper part (notum) of the prothorax, the front segment of the thorax. Along the center of the pronotum runs the median carina, a raised ridge, which may be intersected by sulci. At the tip of the head, a central dent called the fastigium may be seen, flanked by lateral foveolae, shallow pits bordered by small ridges. These features, often visible with a hand lens, are key to distinguishing between closely related species within the subfamily.

Adult four-spotted grasshoppers are usually green or brown with black, white, and ivory markings. Even though they’re called “four-spotted,” they can have anywhere from three to five dark spots on their front wings, sometimes with jagged edges that look like jack-o’-lantern teeth. They have big, wide heads and bodies without a slanted face, and from above, you can see two black triangles on their back. Their back legs are banded, with orange lower legs and black where the upper and lower parts meet.

Nymphs start off with ivory-colored heads and dark stripes near their eyes. As they grow, their heads turn green, and the dark bands fade and become patchy. They also develop a light-colored ridge on their back and show a diagonal ivory line on their shoulder area. Older nymphs can have tan, gray, or pink lower legs.

Identification details

Despite its name, the four-spotted grasshopper can have three to five spots on the forewings. The spots can be discrete of a crenulate pattern—often compared to jack o’ lantern teeth. It is a striking species that is generally green or brown with black, ivory, and white markings. Adult P. quadrimaculatum lack a slanted face. Their head and pronotum appear to be slightly oversized and broad. When viewed from above the pronotum has two black triangles. Their lateral foveolae aren’t visible. The hind femur is banded and the hind tibiae are orange. The junction of the hind femora and tibiae is black. The pronotum disk contains a medium carina that is broken in the middle. While the lateral carinae is clearly visible, it is constricted in the central region. Wing length ranges, with some wings extending just short of the abdomen to others extending 5 mm past the abdomen. Populations found in the southern range of this species, in areas such as Texas, have more common occurrences of longer wings.

Nymphs of these species can be identified by their relatively large, and moderately slanted-faced head. Their antennae are filiform. Initially, first instar nymphs have an ivory colored head, with various bands and stripes around their compound eyes. This ivory turns into green from instar 2 to 5. As these nymphs develop, the dark brown band below their compound eye begins to fade and appear segmented, and a vertical ivory band appears below the compound eye. Their lateral carinae are ivory-colored and become increasingly constricted toward the central region, a trait that is more pronounced in adults of this species. On the anterior central region, there is a pronotal lobe with a diagonal ridge that is ivory. The later instars show a hind tibia that is tan and gray, or sometimes pink.

Identification details

Instar	Color	Wings	Body length	Hind femur	Antennal segment number	Description
Egg pods			seven-eighths to one inch long
Eggs	Tan		4.8 to 5.2 mm			laid in clutches of 6 to 14 eggs
1	green or tan		4.8-6.2 mm	3-3.2 mm	12-13	Dark brown vertical stripe below compound eye and horizontal band behind compound eye; hind femur and medial area almost wholly fuscous
2	green or tan		6.8-7.5 mm	4-4.4 mm	15-16	Green head color; vertical ivory band below compound eye; hind femur and medial area almost wholly fuscous
3	green or tan		8-9.1 mm	5.2-5.4 mm	18-19	Green head color; vertical ivory band below compound eye; hind femur and medial area almost wholly fuscous
4	green or tan		10.7-12 mm	7-7.6 mm	21-22	Green head color; vertical ivory band below compound eye; partly green hind femur
5	green or tan		14.5-18.5 mm	9.3-10.2 mm	23	Green head color; vertical ivory band below compound eye; partly green hind femur
Adult males	green or brown with black, white, and ivory markings		14.5-15 mm	9.3-9.9 mm	22-24
Adult females	green or brown with black, white, and ivory markings		18.5-21.5 mm	11-13 mm	23-24

Featured identification resources

• 
  Band-winged grasshoppers of the Canadian Prairies and Northern Great Plains
• 
  ARS species fact sheet Fourspotted Grasshopper
• 
  Common Wyoming Pest Grasshoppers

All identification resources

Name	Year published	Resource link	Descriptive keyword	Language	Geographic purview	Author	Year published
Common Wyoming pest grasshoppers			Life cycle, Species identification, Biodiversity, Grasshoppers	English		University of Wyoming, Scott Schell, Alexandre Latchininsky, B.A. Shambaugh
Field Guide to Common Western Grasshoppers	2002		Species identification	English		United States Department of Agriculture, Robert E. Pfadt	2002

Distribution

The four-spotted grasshopper is broadly distributed across the western Great Plains from Canada prairies to central Mexico. Although these individuals have been rare in Alberta and Saskatchewan, their populations in these regions have been increasing in recent years.

Biology

Four-spotted grasshoppers produce one generation annually. Considered part of the intermediate hatching group, the hatching lasts for two to three weeks. Adults are found from July to September in most regions and generally remain in the locations they were hatched. Copulation begins with males chasing females, drawn by their movement. The female stops movement to signal copulation, and males begin by tipping their hind femora and stridulating. Females can reject the males mounted on them, as they are able to stridulate by shaking their hind femora in a vertical position. Females oviposit in the soil, laying a clutch of 6 to 14 eggs within an egg pod.

Habitat and Ecology

The four-spotted grasshopper occupies shortgrass, mixed grass, desert, and bunchgrass prairie ecosystems. This species almost exclusively feed on grasses, with 89 to 100 percent of their diet consisting of blue grama for adults and nymphs. Individuals feed on green leaves by either climbing onto the plant and feeding on it about one inch below the tip, working their way down or sitting diagonally to the plant and feeding on the ends of the leaf and working their way towards the base. This type of feeding method produces plant litter which exacerbates competition with rangeland livestock.

The four-spotted grasshopper is a ground-dwelling species. At night, both nymphs and adults rest lying flat on small patches of bare soil or plant litter, typically bordered by blue grama and threadleaf or needleleaf sedge. One to two hours after sunrise, grasshoppers bask by positioning their bodies sideways to the sun. As temperatures rise above 70°F, they become active, feeding, mating, and moving until it gets too hot. When the soil surface temperature reaches around 100°F, grasshoppers lying flat on bare ground shift into a stilt posture, lifting their bodies as high as their legs allow. As temperatures climb further, reaching 120°F, they move up above the ground onto plants and orient themselves toward the sun. This behavior helps them avoid the heat of the ground while minimizing the amount of body surface exposed to direct sunlight; they may also spread their hind legs to aid in cooling.

Land-Use Change

The four-spotted grasshopper is not a long-distance flyer. Their evasive flights extend to 2.5 to 5 feet in distance and can reach 6 inches off the ground. They fly straight and silently, landing to face away from the threat. Evidence that this species occasionally disperses comes from observations in a mixed-grass prairie in eastern Wyoming, where it once reached a density of 7 nymphs per square yard. In 1970, an insecticide treatment over 840 acres nearly eradicated the local population. The species did not reappear until 1973, when a single female was found, followed by two nymphs the next year. These findings suggest the population was able to reestablish itself through dispersal and gradually began to recover.

Pest status

This species is generally subdominant in rangeland areas. In dominant years where densities can range up to 5 young adults per square yard. However, it is one of the top dozen species monitored by USDA Animal and Plant Health Inspection Service (APHIS) because of its impact on rangelands in assemblages.

Parasitism may be a particularly significant cause of mortality for four-spotted grasshoppers. These parasites more frequently attack adults, than nymphs in various stages of development. Seasonal parasitism may occur from July to September, when nymphs are far into their development or when adults start to occur. Natural predators of parasites that threaten grasshopper species include predatory Asilidae and spiders. These organisms, along with weather conditions, help maintain parasitism and in turn grasshopper parasitism.

The four-spotted grasshopper does not readily feed on carbaryl bait.

Outbreaks

In 1955, there was a major grasshopper outbreak in western Oklahoma rangeland where P. quadrimaculatum was one of the dominant species along with Ageneotettix deorum, Aulocara elliotti, Boopedon nubilum.

In 1956, P. quadrimaculatum was one of the dominant species during a grasshopper irruption on the desert prairie of San Rafael Valley, Arizona. Alongside several other species, it contributed to significant grass forage loss across the affected area.

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