Form and function
- Related Topics:
- ice bug
- phasmid
- Orthoptera
- Dictyoptera
- Exopterygota
Adaptive features
Movement
Hind legs of Orthoptera, though useful in walking, are used primarily for leaping. Particularly important are the large muscle in the femur, the hinged attachment of tibia to femur, and the tendon extending within the leg from the femur to the end of the tarsus. In a few semi-aquatic Orthoptera, the hind tibia is broadened as a paddle or equipped with fringed spurs to permit effective swimming strokes in water.
Several orthopterans, including mole crickets, false mole crickets, and sand cricketsare notable burrowers and their legs, especially the front tibiae, are short and strong, with heavy spurs. Small tunnels serve as shelter and as egg-laying locations, and roots or tubers encountered while burrowing are sometimes used as food. Several genera of camel crickets (Gryllacrididae) in the southwestern U.S. have conspicuous, sometimes basket-shaped, clusters of spurs on the hind legs. They often live on sand dunes and burrow chiefly for shelter. A few desert-living grasshoppers, some in the southwestern U.S., others in Africa, exhibit what has been called “self-burial.” Instead of making an elongated cylindrical burrow, the grasshopper rests on the surface of the sand or moves forward and backward, maneuvering its legs until it has submerged itself and covered its body with sand. The apparent purpose is protection.
Body shape is important to many orthopterans, either allowing them to live in places where adequate shelter from weather and enemies is provided or affording them concealment through camouflage. Several katydids and grasshoppers resemble leaves; some are green or brown, others have spots that resemble leaves affected by plant diseases. There are some slender grasshoppers that live among grasses, where they conceal themselves by clinging lengthwise to stems and remaining motionless or by quickly sidling around behind stems.
Camouflage
There are two basic types of insect colors. Structural colors occur when irregular cuticle or scale surfaces break up and reflect certain wave lengths of light. Metallic lusters of some orthopterans (e.g., silvery patches on some grasshoppers) are examples. Most orthopteran colors are due to pigments; often they are located in the cuticle, but sometimes they occur in some deeper body layer. The pigments may be naturally occurring ones or, like melanin, dependent on an oxidation process or a hormonal balance that influences metabolism; these latter pigments are present in varying amounts in different individuals of the same species.
Among some orthopterans, especially grasshoppers, body colors tend to simulate the color of the habitat background. This is particularly true of species inhabiting rocky or sandy environments. In some cases, color changes occur rapidly; this was demonstrated by certain light gray African grasshoppers that became black after being caged a few days on dark burnt-over ground. In other cases more time is required. Color changes usually involve the effect of bright light on integumentary pigments. Among some orthopterans, however, light must enter the eyes, and a rhythm related to some nervous-endocrine mechanism is apparently involved.
An unusual and rapid color change occurs in an Australian alpine grasshopper (Kosciuscola tristis), which lives at above 1,520 meters (5,000 feet) elevation. The adult male, bright greenish blue on the upper part of its body at temperatures above 25 °C (77 °F), is dull and blackish below 15 °C (59 °F). At intermediate temperatures, correspondingly intermediate shades of color occur. Detailed experiments by Australian entomologists prove that temperature, not light intensity, relative humidity, or degree of crowding is the controlling factor. The epidermal cells of the integument contain brown and blue granules; at warmer temperatures on sunny days the blue granules, in a discrete layer uppermost in the epidermal cells, are near the surface of the integument. At night or on cloudy days, the brown granules migrate from the bottom of the epidermal cells and change places with the blue granules. Thirty minutes is sufficient time for a color change to take place.