Lab 4.  Morphology Part 1: Insect External Anatomy

In this lab you will examine a preserved grasshopper and learn to recognize and identify the various parts of an insect’s body.

Objectives

The main objectives of this lab are to help you:

1. learn to recognize and identify sclerites, sutures, and other external features of an insect’s body
2. correlate structure with function in the legs, wings, and antennae of representative insects
3. distinguish different types of mouthparts and explain how they are adapted for different kinds of food
4. Turn in the “10 Orders Collection”, worth 20% of your Insect Collection points.

Activities

1. Review

Before lab, briefly review the materials below to be prepared for viewing specimens.

2. Materials for Lab

**TURN IN: the “10 Orders Collection”, worth 20% of your Insect Collection points.**

For other materials see the list at the bottom of this page

3.   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.

• Head
• Antennae
• Mouthparts
• Thorax
• Legs
• Front wing
• Hind wing
• Abdomen

4.   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.

5.   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.

• Filiform = thread-like
• Moniliform = beaded
• Serrate = sawtoothed
• Setaceous = bristle-like
• Lamellate = nested plates
• Pectinate = comb-like
• Plumose = long hairs
• Clavate = gradually clubbed
• Capitate = abruptly clubbed
• Aristate = pouch-like with one lateral bristle
• All of these

6.   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.  Visit the Mouthparts page in BugBytes to learn about the differences between mandibulate and haustellate mouthparts. Then launch the Mouthparts Tutorial (click below) 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.

7.   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.

8.   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:

• Coxa
• Trochanter
• Femur
• Tibia
• Tarsus — usually subdivided into 1-5 tarsomeres

The term pretarsus refers to the terminal segment of the tarsus and any other structures attached to it, including:

• ungues — a pair of claws
• arolium — a lobe or adhesive pad between the claws
• empodium — a large bristle (or lobe) between the claws
• pulvilli — a pair of adhesive pads

Thoracic legs are often adapted for special functions.   Their structure may provide clues to other aspects of an insect’s biology.  Learn to recognize and identify the following leg modifications:

• Saltatorial — jumping
• Raptorial — seizing
• Fossorial — digging
• Natatorial — swimming
• Cursorial — running

9.   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):

• Costa (C)
• Subcosta (Sc)
• Radius (R)
• Media (M)
• Cubitus (Cu)
• Anal veins (A)

Cross veins: Names of crossveins are based on their position relative to longitudinal veins:

• Humeral (h)
• Radial (r)
• Sectorial (s)
• Radio-medial (r-m)
• Medial (m)
• Medio-cubital (m-c)
• Cubito-anal (cu-a)

Wings may also be adapted or modified for special functions.   Be sure you can recognize and identify each of these adaptations:

• Tegmen / Tegmen Close-Up
• Elytra / Elytra Close-Up
• Hemelytra / Hemelytra Close-Up
• Halteres / Halteres Close-Up
• Hamuli / Hamuli Close-Up
• Frenulum / Frenulum Close-Up

Materials

You will need the following for this lab:

• Smartphone or computer
• Lab 4 Handout
• Preserved grasshopper; honeybee (or other bee); milkweed bug (or another large hemipteran); mosquito; housefly; moth or butterfly
• Stereoscopic microscope or hand lens
• Dissecting scissors, or scalpel, or single-edged razor blade
• Insect pins or dissecting needles
• Small forceps or tweezers