Little spur-throated grasshopper (Melanoplus infantilis)

Melanoplus infantilis Little spur-throated grasshopper
Distribution
British Columbia, Alberta, Saskatchewan, Manitoba, Washington, Oregon, Idaho, Utah, Arizona, Montana, Wyoming, Colorado, New Mexico, North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Minnesota, Iowa
Taxonomy
Family:	Acrididae
Subfamily:	Melanoplinae
Genus:	Melanoplus
Additional resources
Full taxonomy at OSF

The little spur-throated grasshopper (Melanoplus infantilis) is the smallest species within the Melanoplus genus. It is widely distributed across western North America, particularly in the rangelands of the Northern Plains. Although not consistently damaging, it is considered a pest in these areas, and often the most numerically abundant species in Canadian grasslands.

Nomenclature

Melanoplus infantilis Scudder, 1878. For full nomenclature, see this taxon's page on Orthoptera Species File

Identification

The little spur-throated grasshopper is a species of spur-throated grasshoppers, a dominant group in North American grasslands known for their abundance, activity, and diversity. Most North American spur-throated grasshoppers belong to the subfamily Melanoplinae, recognized by a spiny projection on the prosternum between the front legs, roughly where a throat would be. This subfamily includes the migratory grasshopper (Melanoplus sanguinipes), one of the most widespread and well-known species on the continent. Melanoplinae is also the most diverse grasshopper subfamily, with hundreds of species adapted to a wide range of environments—from arctic tundra to tropical forests, and from alpine meadows to deserts.

Most species complete their life cycle in a year, with eggs overwintering in the soil. However, the group shows remarkable variation in habitat use and diet. It includes both flightless species confined to meadows and mountain peaks, and powerful long-distance fliers like M. sanguinipes and the now-extinct Rocky Mountain locust (Melanoplus spretus).

Melanoplus infantilis adults are small brown or gray grasshopper with patches of lighter and darker colors to help it blend into its surroundings. It has a slightly curved head, big eyes, and pale yellow antennae that get darker at the tips. Its body is smooth with faint ridges, and has long wings that stretch past its back end. The back legs are yellow underneath and rusty red or dark brown on top, with spots and pale stripes, while the lower parts of the legs are pale blue fading to yellow near the ends. Nymphs are creamy white with dark marks on their faces and thin, thread-like antennae, with a pale crescent-shaped mark below their eyes like the adults.

This species is identifiable by the small staghorn-shaped cerci at the tip of the male’s abdomen. After the males are identified, females can be distinguished from other Melanoplus species by comparing their size and markings.

Identification details

The little spur-throated grasshopper is brown or grayish with different shades of dark and light colors, which helps it blend into its environment.

It has a large, slightly arched head, with the face and sides colored brown-olive or yellow, spotted with black marks. The big, prominent eyes sit on either side of the vertex which is just a little wider than the base of the antennae. A yellow-edged postocular band is hard to see on the head but is visible from the side lobes of the prozona and can change as the grasshopper grows. Near the base of the antennae is a pale crescent-shaped fastigium, which is wider than the space between the eyes. The antennae themselves are tan or pale yellow, darkening at the tips, and about 5 mm long.

The pronotum looks smooth and similar in size to the rest of the body. It has a noticeable median carina, especially on the back part, and distinct, blunt lateral carinae. The transverse sulci run across the front part of the pronotum but don’t cross the median ridge.

The abdominal terga are dark on the sides and base. Their tegmina usually extend beyond the abdomen and the tip of the hind femora. The tegmina are ash-gray with yellowish and dark brown spots. The hind femora are yellow underneath and dark brown or rusty red on top, marked with two dark spots and pale angled bars near the base. The hind tibiae are mostly pale blue, lighter at the base and yellowish near the tip. The hindwings are clear.

Females have a deep notch on the underside of the abdomen and slender cerci with concave edges. Males have a distinctive forked cercus with a small projection and a long, pointed ventral arm that tapers sharply. They also have a triangular supraanal plate with a deep groove down the middle and a notched subgenital plate.

Nymphs are usually creamy white with distinct dark lines on the face, including one running from below the eye to the mouth and a dark ridge between the eyes. Their heads are vertical with a slightly slanted face and filiform antennae. The antenna segments near the front are ringed with white, and their compound eyes have pale speckles. The crescent-shaped mark seen on adults is also on nymphs, located on the gena beneath the eyes and extending onto the sides of the head. The underside of the thorax and abdomen is usually pale yellow or white.

Identification details

Instar	Color	Wings	Body length	Hind femur	Antennal segment number	Description
Eggs	Pale tan		3.9 mm to 4.2 mm in length 1.1 mm in diameter
Egg pod			22.2 to 25.4 mm			Contains 10 to 13 eggs that arranged in two columns at the bottom
1	creamy white with dark marks		4.2-5.2 mm	2.1-2.3 mm	13
2	creamy white with dark marks		4.6-7.2 mm	3-4.3 mm	15-18
3	creamy white with dark marks		7.1-10.1 mm	4.9-5.7 mm	19-20
4	creamy white with dark marks		9.1-12.1 mm	6.3-7.8 mm	20-22
5	creamy white with dark marks		12-15 mm	8.4-9.2 mm	22-25
Adult males	brown or gray	hindwings are clear	16.5-17 mm	9.6-10.7 mm	25-26
Adult females	brown or gray	hindwings are clear	16-19 mm	10.5-11.2 mm	24-25

Featured identification resources

• 
  Spur-throated grasshopper of the Canadian Prairies and Northern Great Plains
• 
  ARS species fact sheet Little Spurthroated Grasshopper
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  Pest grasshoppers in Oregon
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  Common Wyoming Pest Grasshoppers

All identification resources

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Distribution

The little spur-throated grasshopper is found across the northern Rocky Mountain region and northern Great Plains, with its range stretching from Minnesota and Manitoba in the east to British Columbia and Montana in the west, and as far south as Nebraska and Colorado . It is especially common in central Colorado.  In Nebraska, this species occurs throughout the panhandle and western parts of the state , where it is the smallest Melanoplus species living in the rangeland areas.  This species is also abundant throughout the grasslands of Wyoming.

Biology

The little spur-throated grasshopper is univoltine and overwinters in the egg stage.  Eggs hatch early in mid-spring, with peak hatching typically in mid June . The hatching period lasts about three weeks . Nymphs are present from June through August, and adults typically appear in August through October.  Development from nymph to adult takes about 35 days—faster than many other pest species, likely due to the insect’s small size.  Growth is rapid in the first three instars, with the fourth and fifth instars each taking about five days to complete . Each female typically lays around 10 to 13 eggs per pod. 

Habitat and ecology

Melanoplus infantilis is typically found in open rangelands, preferring dry, grassy environments with sandy or gravelly soils.  It inhabits areas with sparse, pale vegetation and treeless plains, as well as foothills and mountainous regions up to elevations of 10,000 feet.  This species also occurs in mixed grass and shortgrass prairies and the dry, grassy zones of montane coniferous forests and parklands within the northern Canadian forest region. 

It is a polyphagous feeder consuming both grasses and forbs depending on its environment.  However, in lab studies, M. infantilis showed forb feeding preferences. When presented with dandelion, blue grama, western wheatgrass, and alfalfa, they preferred dandelion. However, when given dandelion and downy brome, they consumed both equally. They are known pests in grassland ecosystems, especially in crested wheatgrass pastures . Major grass hosts include blue grama, western wheatgrass, needleandthread, sand dropseed, Idaho fescue, Parry oatgrass, and various bluegrass species. Grass-like plants such as threadleaf sedge and needleleaf sedge are also important food sources. Key forbs consumed include scarlet globemallow, woolly plantain, broom snakeweed, fringed sagewort, Fendler sandwort, dandelion, and several milkvetch species. Adults may feed on plant litter from the ground.

They often interact with their surroundings by climbing tall plants such as Verbena stricta and Oenothera species.  Damage occurs when they feed on young native grasses before they reach the 3.5-leaf stage, a critical point for healthy plant development.  Adult development typically overlaps with this stage over an eight-day period. 

To warm up in the morning, M. infantilis basks on bare ground or low vegetation such as blue grama, exposing their sides to the sun. Basking begins about an hour after sunrise and may include subtle movements like shifting position or raising and lowering the body.  When temperatures climb near 115°F, adults escape the heat by climbing about 2 inches up grass stems and resting vertically, head-up, on the plant. 

At low population densities (0.1 to 0.5 per square yard), adults tend to stay within the same habitats they occupied as nymphs. At night, they rest on the ground or on low shrubs.  They have also been seen climbing 5 to 10 inches up silver sagebrush or broom snakeweed at night.  Although M. infantilis is capable of migrating and occasionally shows up in cities and towns.  it usually makes short, quick flights only when disturbed. These flights are silent, straight, and cover about 3 to 10 feet in distance and 4 to 9 inches in height . No migratory bands of nymphs have been observed in this species. 

Due to their small size, M. infantilis are a significant food source for songbirds.

Pest status

The little spur-throated grasshopper is one of the top dozen species monitored by USDA Animal and Plant Health Inspection Service (APHIS) because of its impact on rangelands.

Outbreaks

Melanoplus infantilis is often overlooked because of its small size, but it can still cause notable damage to rangeland ecosystems.  In most areas, population densities remain below one grasshopper per square yard. However, during favorable conditions, outbreaks can occur, with numbers rising to 20  to 40 individuals per square yard.  These outbreaks make M. infantilis a species of economic concern, as it feeds heavily on forage grasses.  Fortunately, it tends to avoid forbs that are commonly grazed by livestock, making it less harmful than some other pest grasshoppers.  In field trials on western wheatgrass in Montana, adults were shown to consume about 35 mg of dry forage per day.  In the grasslands of Alberta and Saskatchewan, it is frequently the most abundant grasshopper species present. 

In 1953, it was the most abundant species at 11 out of 42 sites surveyed in Montana’s mixed-grass prairie.

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