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Grasshoppers

Goggy Davidowitz

Observant hikers in the Sonoran Desert soon notice grasshoppers jumping near their feet or flitting between bushes and cacti. These are among the most frequently encountered and easily observed of the Sonoran Desert insects in the late summer.

Grasshoppers have a fairly simple body design. The rounded head capsule contains the compound eyes, chewing mouth parts, and the short thread-like antennae, which are always shorter than the body (hence the name “short-horned” grasshoppers, in contrast to another suborder, the katydids or “long-horned” grasshoppers). The middle thoracic segments and part of the abdomen are covered by a shield-like pronotum that extends from the first thoracic segment. The forewings are leathery and not used for flight. Instead they protect the delicate hind wings, which are folded accordion-like beneath the forewings until they are unfolded for flight. However, all immature stages and the adults of many species lack wings altogether and cannot fly.

The most noticeable feature of grasshoppers is their long, jumping hind legs, which enable them to leap well over 20 times their body length (imagine a 6-foot tall person jumping 120 feet!). However, while the powerful jumping muscles of the hind legs provide the force necessary for leaping, they cannot propel the grasshopper in these impressive leaps unaided. Most of the kinetic energy to do this comes not from the muscles, but from the semilunar crescent located in the knee of the hind leg. This crescent-shaped organ is made of elastic fibers that store energy in preparation for a jump; they release this energy explosively, propelling the grasshopper forward many times its body length.

Grasshoppers develop through incomplete metamorphosis. The nymphs appear similar to the adults except that they lack wings and have incomplete reproductive organs. The number of instars (larval stages between molts) through which a grasshopper develops before reaching adulthood is fixed in some species (typically 4 to 6). In others, it depends on growing conditions: the better the conditions, the fewer the immature stages.

Life History and Ecology

Most Sonoran Desert short-horned grasshoppers spend the winter months in the soil as eggs. These are laid in clutches from just a few to well over a hundred eggs, depending on the species. The eggs are enclosed in an egg pod made of a frothy material that protects them from parasites, desiccation and mechanical hazards. Grasshoppers hatch during 2 separate seasons in the Sonoran Desert. The smaller winter cohort (all members of a population hatching at about the same time) emerges from the egg stage after the winter rains, maturing to adults in April to May. The much larger summer cohort emerges after the monsoon rains, leading to a peak in adult abundance from late August to early October. The number of generations per year for many species depends largely on the duration and quantity of the summer monsoons. For example, the pallid-winged grasshopper (Trimerotropis pallidipennis) can produce two or three generations a year in a good rainy season, but only one or none at all in dry years.

Male grasshoppers attract females both visually and acoustically. Males of banded-winged grasshoppers (subfamily Oedipodinae) can typically be seen in the summer taking short flights, flashing their brightly-colored wings, snapping them together, or both, producing a distinct sound. These short flight noises are called crepitation; the sounds are usually species-specific. Males also attract females by stridulation (scraping the hind femora against the forewing); this too produces species-specific mating sounds. Not all sounds produced by grasshoppers function solely to attract females, however. While hiking in the Sonoran Desert, one is likely to hear short bursts of clicks emanating from a creosote bush. This incessant clicking comes from a male desert clicker (Ligurotettix coquilletti); it spends much of its life on a single creosote bush claimed as a territory, stridulating to warn away other males as well as to attract females.

 
Order: Orthoptera
Suborder: Caelifera (short-horned grasshoppers)
Family: Acrididae
Subfamilies and species discussed:
     Acridinae (Slant-faced grasshoppers)
          Achurum spp.
          Mermiria spp.
     Cyrtacanthacridinae (spur-throated grasshoppers)
          Schistocerca nitens (gray bird grasshopper)
          Schistocerca shoshone (green bird grasshopper)
     Gomphocerinae (tooth-legged grasshoppers)
          Bootettix argentatus (creosote bush grasshopper)
          Ligurotettix coquilletti (desert clicker)
     Melanoplinae
          Dactylotum variegatum (harlequin or rainbow grasshopper)
     Oedipodinae (banded-winged grasshoppers)
          Trimerotropis pallidipennis (pallid-winged grasshopper)
     Romaleinae (lubbers)
          Taeniopoda eques (horse lubber)
          Brachystola magna (plains lubber)
Suborder: Ensifera (long-horned grasshoppers)
Family: Tettigoniidae
          Insara covilleae (creosote bush katydid)
 

Feeding

About 70 percent of herbivorous insects eat only one or a few species or genera of plants. In contrast, grasshoppers are generalist feeders, eating plants from an extremely broad range of families. Grasshoppers tend to grow better and produce more offspring when their diet consists of a mixture of plants. But different species go about this in very different ways. The gray bird grasshopper (Schistocerca nitens) and the green bird grasshopper (Schistocerca shoshone) are cryptically colored, avoiding predators by spending most of the day on a single host plant. (Bird grasshoppers are so-named because they are among the largest of the Sonoran grasshoppers, with the females reaching 6.5 cm [2½ inches] in length.) They obtain the necessary dietary mixtures after feeding for a long period on one host species, by eventually shifting to another. In contrast, the horse lubber (Taeniopoda eques) and the harlequin or rainbow grasshopper (Dactylotum variegatum) also eat a wide variety of plants, but switch frequently, taking a nibble here and a nibble there.

Not all grasshoppers are generalist plant-eaters, however. The creosote bush grasshopper (Bootettix argentatus) is the only one among the more than 8000 species of grasshoppers worldwide that eats a single species of plant—the creosote bush. Hiking in the desert scrub one is likely to come upon another exception, a large (8 cm [3¼ inches]), heavy-bodied, flightless grasshopper, the plains lubber (Brachystola magna). This short-winged grasshopper is a generalist herbivore, yet it has recently been shown to be predacious as well, pouncing on and eating other grasshoppers and insects.

Predator Avoidance

Grasshoppers employ a wide range of mechanisms to keep from being eaten. The foremost of these is crypsis, matching the background in color or texture. This is most evident in the banded-winged grasshoppers. These ground-dwelling grasshoppers superbly match the color of the soil they live on. In some species, such as the pallid-winged grasshopper, populations living on red soil have a predominantly reddish color, those living on white soil are white, and those on dark or black soil are dark brown or black. These differences can be seen over distances of only a few hundred meters. Species of the genera Achurum and Mermiria in the subfamily Acridinae (commonly called the slant-faced grasshoppers because their faces are positioned obliquely to the rest of the body) live and feed on grasses. They are long and slender and typically have bands running the length of the body, mimicking grass stalks. The casual observer will be hard-pressed to notice one of these insects clinging to a stalk of grass.

Banded-winged grasshopper
Banded-winged grasshopper

The creosote bush grasshopper is another excellent example of crypsis. This species eats only the leaves of the creosote bush and spends all its time among them. It is olive green, with shiny, pearly spots mimicking the green leaves with their shiny, oily secretions. The creosote bush katydid (Insara covilleae), in a separate suborder of long-horned grasshoppers, also lives solely on creosote bushes; it too is olive green with pearly, shiny patches—a fine example of convergent evolution.

Banded-winged grasshoppers take a different approach to escaping predators. Their hind wings are often brightly colored with red, orange, yellow, or white bands, in sharp contrast to the often drab brown of the forewings. When startled by a predator (or hiker), they take to the air. The predator focuses attention on the brightly colored and flashy hind wing, only to have the grasshopper disappear from sight when it folds its wings, lands, and again cryptically blends into the background.

Rather than hiding, some grasshoppers actually advertise their presence to predators. A hiker in the Sonoran Desert is likely to come upon the horse lubber (Taeniopoda eques), a large (6.5 cm [2½ inches]), black heavy-bodied grasshopper with yellow or orange stripes and antennae, greenish veins on the forewings, and pinkish-red hind wings. The harlequin or rainbow grasshopper (Dactylotum variegatum) is smaller (3.5 cm [1¼ inches]), short-winged, and black with bright blue, red, yellow, and white markings. These species sequester toxins from the plants they eat, making them unpalatable for most predators. Their aposematic (warning) coloration informs potential predators that they are poisonous—stay away!

Katydid or Grasshopper?

“It’s green. It must be a Katydid!”

Although it’s true that katydids are often green, there are some other ways to tell them apart from grasshoppers. For one thing, their appearance is different. Katydids have long antennae and sword-like ovipositors; grasshoppers have short antennae and blunt ovipositors. (The ovipositor is the egg-laying structure at the hind end of the abdomen of the female.) Another difference is in their egg-laying behavior. Katydids lay their eggs in plants whereas grasshoppers lay theirs in the ground.