grasshopper

Grasshoppers are herbivorous insects of the suborder Caelifera in the order Orthoptera. To distinguish them from bush crickets or katydids, they are sometimes referred to as short-horned grasshoppers. Species that change colour and behaviour at high population densities are called locusts.

Characteristics

The Caelifera have antennae that are almost always shorter than the body (sometimes filamentous), and short ovipositors. Those species that make easily heard noises usually do so by rubbing the hind femurs against the forewings or abdomen (stridulation), or by snapping the wings in flight. Tympana, if present, are on the sides of the first abdominal segment. The hind femora are typically long and strong, fitted for leaping. Generally they are winged, but hind wings are membranous while front wings (tegmina) are coriaceous and not fit for flight. Females are normally larger than males, with short ovipositors.

They are easily confused with the other sub-order of Orthoptera, Ensifera, but are different in many aspects, such as the number of segments in their antennae and structure of the ovipositor, as well as the location of the tympana and modes of sound production. Ensiferans have antennae with at least 30 segments, and caeliferans have less. In evolutionary terms, the split between the Caelifera and the Ensifera is no more recent than the Permo-Triassic boundary (Zeuner 1939).

Diversity and range

Recent estimates (Kevan 1982; Günther, 1980, 1992; Otte 1994-1995; subsequent literature) indicate some 2,400 valid Caeliferan genera and about 11,000 valid species described to date. Many undescribed species exist, especially in tropical wet forests. The Caelifera are predominantly tropical but most of the superfamilies are represented world wide.

Families

The Sub Order consists primarily of five major families:

• Acrididae (field grasshoppers and locusts)
• Eumastacidae (monkey grasshoppers)
• Tanaoceridae (tanaocerids)
• Tetrigidae (grouse locusts, pygmy grasshoppers, and pygmy locusts)
• Tridactylidae (pygmy mole crickets)

The most important family is Acrididae, consisting of about 10,000 species. The family is characterised by the short, thickened antennae and relatively unmodified anatomy; they are often visually more striking than other Caelifera, due to the adults' wings and legs, which are well developed and may be brightly coloured. As well as singing by rubbing their legs against the wings/abdomen, there may also be a visual display. The Acrididae includes the locusts, which can be serious economic pests.

Eggs are commonly laid in the ground with a foamy substance around them to protect them during incubation; typically the number of eggs laid by a female is between 400 and 500.

Biology

Digestion and excretion

The digestive system of insects includes a foregut (stomodaeum - the mouth region), a hindgut (proctodaeum - the anal region), and a midgut (mesenteron). The mouth leads to the muscular pharynx (which sucks and swallows), and through the esophagus to the crop. This discharges into the midgut, which leads to the malpighian tubules. These are the chief excretion organs. The hindgut includes intestine parts (including the ileum and rectum), and exits through the anus. Most food is handled in the midgut, but some food residue as well as waste products from the malpighian tubules are managed in the hindgut. These waste products consist mainly of uric acid, urea and a bit of amino acids, and are normally converted into dry pellets before being disposed of.

The salivary glands and midgut secrete digestive enzymes. The midgut secretes protease, lipase, amylase, and invertase, among other enzymes. The particular ones secreted vary with diet.

Nervous System

The grasshopper's nervous system is controlled by ganglia, dense groups of nerve cells which are found in most animals more advanced than cnidarians. In grasshoppers, there are ganglia in each segment as well as a larger set in the head, which are considered the brain. There is also a neuropile in the centre where all of the ganglia channel signals through. The sense organs (sensory neurons) are found near the exterior of the body and basically consist of tiny hairs (sensilla), consists of one sense cell and one nerve fiber, which are each specially calibrated to sense a certain thing. While the sensilla are found all over the body, they are most dense on the antennae, palps (part of the mouth), and cerci (near the posterior end). Grasshoppers also have tympanal organs for sound reception; both these and the sensilla are linked to the brain via the neuropile.

Reproduction

The grasshopper's reproductive system consists of the gonads, the ducts which carry sexual products to the exterior, and accessory glands. In males, the testes consist of a number of follicles which hold the spermatocytes as they mature and form packets of elongated spermatozoa. After they are liberated in bundles, these spermatozoa accumulate in the vesicula seminalis (vas deferens).

In females, each ovary consists of ovarioles. These converge upon the two oviducts, which unite to create a common oviduct which carries ripe eggs. Each of the ovarioles consists of a germarium (a mass of cells that form oocytes, nurse cells, and follicular cells) and a series of follicles. The nurse cells nourish the oocytes during early growth stages, and the follicular cells provide materials for the yolk and make the eggshell (chorion).

During reproduction, the male grasshopper introduces sperm into the vagina through its aedeagus (reproductive organ), and inserts its spermatophore, a package containing the sperm, into the female's ovipositor. The sperm enters the eggs through fine canals called micropyles. The female then lays the fertilized egg pod, using her ovipositor and abdomen to insert the eggs about one to two inches underground, although they can also be laid in plant roots or even manure. The egg pod contains several dozens of tightly-packed eggs that look like thin rice grains. The eggs stay there through the winter, and hatch when the weather has warmed sufficiently. In temperate zones, many grasshoppers spend most of their life as eggs through the "cooler" months (up to 9 months) and the active states (young and adult grasshoppers) live only up to three months. The first nymph to hatch tunnels up through the ground, and the rest follow. Grasshoppers develop through stages progressively get larger in body and wing size. This development is referred to as hemimetabolous or incomplete development since the young are rather similar to the adult.

Circulation and respiration

Grasshoppers have open circulatory systems, with most of the body fluid (hemolymph) filling body cavities and appendages. The one closed organ, the dorsal vessel, extends from the head through the thorax to the hind end. It is a continuous tube with two regions - the heart, which is restricted to the abdomen, and the aorta, which extends from the heart to the head through the thorax. Hemolymph is pumped forward from the hind end and the sides of the body through a series of valved chambers, each of which contains a pair of lateral openings (ostia). The hemolymph continues to the aorta and is discharged through the front of the head. Accessory pumps carry hemolymph through the wing veins and along the legs and antennae before it flows back to the abdomen. This hemolymph circulates nutrients through the body and carries metabolic wastes to the malphighian tubes to be excreted. Because it does not carry oxygen, grasshopper "blood" is green.

Respiration is performed using tracheae, air-filled tubes which open at the surfaces of the thorax and abdomen through pairs of spiracles. The spiracle valves only open to allow oxygen and carbon dioxide exchange. The tracheoles, found at the end of the tracheal tubes, are insinuated between cells and carry oxygen throughout the body. For more information on respiration, see Insect.)

Other information

Grasshoppers as food

In many places around the world, grasshoppers are eaten as a good source of protein. Some countries supposedly instruct military personnel to collect grasshoppers to eat as a food source.

In Korea rice field grasshoppers are eaten as a side dish at meals, as a lunch box ingredient, or as a drinking snack. Many Koreans consider grasshoppers to be a health food. The preparation of grasshoppers as food varies, but sometimes they are pan-fried, with or without oil, after removing the wings and legs. Various cultures also use them as medicines for treatment of convulsions in children, coughs, tetanus, and weakness, though there are no documented pharmaceutical properties.

Locusts

Locusts are several species of short-horned grasshoppers of the family Acrididae that sometimes form very large groups (swarms); these can be highly destructive and migrate in a more or less coordinated way. Thus, these grasshoppers have solitary and gregarious (swarm) phases. Locust swarms can cause massive damage to crops in all continents except Antarctica. See also locust and desert locust. Important locust species include Schistocerca gregaria and Locusta migratoria in Africa and the Middle East, and Schistocerca piceifrons in tropical Mexico and Central America (Mesoamerica). Other grasshoppers important as pests (which, unlike "true" locusts, do not change color when they form swarms) include Melanoplus species (like M. bivittatus, M. femurrubrum and M. differentialis) and Camnula pellucida in North America; the lubber grasshopper Brachystola magna, and Sphenarium purpurascens in Northern and Central Mexico; and species of Rhammatocerus in South America.

External links

• Tree of Life Web Project

Source

• Firefly Encyclopedia of Insects and Spiders, edited by Christopher O'Toole, ISBN 1-55297-612-2, 2002

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