Compare your grasshopper to Figure 1. Use this illustration to familiarize yourself with the various external features of the grasshopper. It is also important to identify the sex of your specimen by the secondary sexual characteristics shown in this illustration. Note the three distinct body regions: the head, thorax, and abdomen.
The head (Figures 1 and 2) is a functional unit that performs various tasks; the major sensory area, the ingestion of food, and it is also the major area of information processing for coordinating body activities. Although the head appears to be composed of one single segment, it is in fact made up from six separate segments that have used into one. The six segments only appear during embryological development.
The grasshopper is a biting/chewing insect and as a result has mandibular mouthparts. The labrum, labium, and maxillae hold food between and against the mandibles which move from side to side to grind food for swallowing. The palpi help manipulate the food and also contain sense organs which serve as taste detectors. Food is further manipulated by the tonguelike hypopharynx (Figure 4). With a dissecting needle probe around the mouth area to identify the various mouth parts and their function. The use of a dissection microscope greatly aids in this.
Insects have compound eyes. This type of eye differs from the vertebrate eye by being made up of hundreds of separate lenses of facets each with its own separate photoreceptor. Together each lens and photoreceptor form a unit called an ommatidium. The exoskeleton is transparent over the eye and forms a protective cornea. Such an eye produces a mosaic type of image. The more ommatidia a compound eye has, the greater the resolution or detail the image forms. In addition to having compound eyes, grasshoppers have three simple eyes called ocelli. These eyes cannot form images but are for sensing changes in illumination. They may also play a role in coordinating the daily rhythms and activities according to the position of the sun.
The antenna are sensory structures for the sense of touch and smell. Insects are often seen moving about with their antenna waving. The antenna are well muscled and flexible structures containing many sensory bristles.
The thorax is the middle section of the grasshopper and is composed of 3 segments: the large shield like prothorax, the mesothorax, and the metathorax. Each of these segments have a pair of legs and can be identified by this. Between each of these segments are a pair of respiratory openings called spiracles. The legs are composed of five segments. The coxa joins the leg to the body, followed by the small trochanter, the large femur, the thin tibia, and clasping tarsus.
The thorax also contains a pair of wings. On most grasshoppers these are well developed and used for flight. On Lubber grasshoppers, however, the wings are small and useless for flight. A secondary fucntion of the grasshopper wing is for producing mating calls. The male grasshopper vibrates his wings together advretising his presence to prospective mates.
Posterior to the thorax is the abdominal section that is composed of eleven segments. The first 8 segments each have a pair of spiracles. The last three segments form the external genitalia of both sexes. The cerci are also found emanating from the 11th segment. The cerci are sensory structures and have numerous touch sensors at their terminal end. Female grasshoppers have a muscular egg laying structure at the end of the abdomen called the ovipositor. The female lays her eggs in the ground with this organ.
