External Anatomy Lab
In this lab you will examine a preserved grasshopper and learn to recognize and identify the various parts of an insect’s body.
The main objectives of this lab are to help you:
- learn to recognize and identify sclerites, sutures, and other external features of an insect’s body
- correlate structure with function in the legs, wings, and antennae of representative insects
- distinguish different types of mouthparts and explain how they are adapted for different kinds of food
You will need the following materials for this lab:
- Preserved grasshopper
- Stereoscopic microscope or hand lens
- Scalpel or single-edged razor blade
- Insect pins or dissecting needles
- Small forceps or tweezers
Lubber grasshoppers (Romalea microptera) are large, heavily sclerotized insects with relatively unspecialized bodies. Like all members of the order Orthoptera, they are herbivores. Their mouthparts are adapted for biting and chewing, and they have large powerful hind legs used for jumping. As adults, lubber grasshoppers have short wings that are incapable of flight. The wings are used to signal receptivity during courtship.
Your grasshopper is preserved in a mixture of alcohol and glycerin. Rinse it thoroughly in running water before examining it under the microscope or hand lens.
1. Gross Anatomy
The insect’s body is divided into three functional regions (tagmata): head, thorax, and abdomen. Appendages of the head include the mouthparts and the antennae. Appendages of the thorax include the legs and the wings.
2. Anatomy of the Head
Find each part of the grasshopper's head listed in your lab printout. Change the view to see the head from different angles. Click on "ZOOM" for a closeup of each structure. Label the diagrams in your lab printout.
3. Types of Antennae
The antennae of insects are modified in many ways. Some of these modifications just provide greater surface area for sensory receptors, while others are unique adaptations that bestow special sensory capabilities, such as detecting sound vibrations, wind speed, or humidity.
You should be able to recognize and distinguish each of the following antennal types.
4. Comparative Mouthparts
All "primitive" insects, such as the grasshopper, have mouthparts adapted for grinding, chewing, or crushing solid food. Some of today's more "advanced" insects, however, have become adapted for ingesting liquid food. They feed in various ways: probing/sipping, sponging/lapping, piercing/sucking, etc. But regardless of function, all mouthparts are constructed from the same five building blocks: labrum, mandibles, maxillae, labium, and hypopharynx. Launch the Mouthparts Tutorial to view an interactive lesson that allows you to compare a grasshopper's mouthparts with those of a ground beetle, dragonfly naiad, honey bee, true bug, mosquito, blow fly, and moth.
5. Thorax and Abdomen
Find each part of the grasshopper's body listed in your lab printout. First, choose a region (thorax or abdomen) and then select an appropriate structure. Click on "ZOOM" for a closeup view. Label the diagrams in your lab printout.
6. Thoracic Legs -- Structure and Adaptations
Most insects have three pairs of walking legs -- one pair on each thoracic segment. Each leg contains five structural components (segments) that articulate with one another by means of hinge joints:
The term pretarsus refers to the terminal segment of the tarsus and any other structures attached to it, including:
|Thoracic legs are often adapted for special functions. Their structure may provide clues to other aspects of an insect's biology. Learn to recognize the following leg modifications:|
7. Wing Modifications and Adaptations
The wings appear to be outgrowths of the tracheal (respiratory) system. The pattern of veins varies from order to order, and even from species to species. Certain consistencies, however, make wing venation a useful tool for insect identification. There are several systems for naming wing veins, but we will adhere strictly to the Comstock-Needham System.
Label each of the following veins on the generalized diagram in your lab printout. No such wing exists, but the naming conventions will be useful later in the course when you begin identifying insects in your collection. At that time, you will receive detailed instructions that pertain to the venation in particular insect orders. For now, try to become familiar with these names and abbreviations.
|Longitudinal veins (anterior to posterior):||Cross veins:|
Wings may also be adapted or modified for special functions. Be sure you can recognize and identify each of these adaptations: