Illinois Natural History Survey - University of Illinois

The Naturalist's Apprentice: What is an Insect?

Michael Jeffords, Center for Economic Entomology

Objective: to learn the basic external anatomy of an insect.


Materials: multiple copies of What Is an Insect?


 Vocabulary: antennae, bilaterally symmetrical, cerci (cercus), ocelli (ocellus), segments, tagmosis


Comments: The basic insect body is a hollow tube made up of segments, and these segments are grouped into three body regions--head, thorax, and abdomen--in a process called tagmosis (tagmosis is the clumping together of individual segments to form different body regions that have a particular function). Insects are also bilaterally symmetrical, that is, one side is exactly the same as the other side. On the head are a pair of antennae, a pair of compound eyes, and several simple eyes (called ocelli). On the thorax, the locomotory part of the insect, we find three pairs of legs and two pairs of wings. Finally, note that on the rear of the abdomen we have a pair of structures that look like antennae. These are called cerci (singular cercus) and tell the insect what's going on at its other end.



1. Present the above material to students before passing out What Is an Insect? or have them try their hands at the diagram with no explanation from you.


2. Go over the completed diagrams as a class and discuss what might be some of the functions carried out by the head (sensory, feeding), thorax (locomotion), and abdomen (digestion, reproduction, respiration).


3. Have students draw an insect that has one or all of the various body parts modified to do different things. For example, have them draw the back legs modified for swimming or the front legs for grasping.


What Is an Insect?


 Fill in the blanks on this diagram with the correct names from the list that follows.


abdomen, antenna, cercus, compound eye, foreleg, forewing, headhindleg, hindwing, middleleg, simple eye (ocellus), thorax


Illinois Natural History Survey

1816 South Oak Street, MC 652
Champaign, IL 61820

Terms of use. Email the Web Administrator with questions or comments.

© 2019 University of Illinois Board of Trustees. All rights reserved.
For permissions information, contact the Illinois Natural History Survey.

Staff Intranet