INVESTIGATION 1 How are Insects Classified?

OVERVIEWLESSON 1: What is an Arthropod?Students begin by sharing their prior knowledge of the classification system. Then they observe specimens belonging to the Phylum Arthropoda to search for common identifying characteristics, and develop a working definition of the term arthropod. They apply their definitions to classify a set of 35 Backyard Invertebrate Cards.RECOMMENDED TIME: 2 Class Sessions

LESSON 2: What is an Insect?Students review what they know about the characteristics that define the Class Insecta, and then use a poster to discuss insects’ structures and their functions. They reclassify the set of cards to sort for insects. Finally, they read the Field Guide to Backyard Invertebrates for more information.RECOMMENDED TIME: 1 or 2 Class Sessions

ASPECTS OF INQUIRYStudents define (4) the terms arthropod and insect. They observe, (3) compare and contrast (3) specimens, and apply (3) their definitions to classify (4) inverte-brates.

BIG IDEASThe classification system provides an orderly method for categorizing biological information and a universal method by which scientists can communicate.

Animals are classified into categories: kingdom, phylum, class, order, family, genus,

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ASPECTS OF INQUIRYFor grades 5 - 8, the National Research Council (NRC) has identified eight “Fundamental Abilities Necessary to Do Scientific Inquiry.” These are:

(1) Identify questions that can be answered through scientific investigations.

(2) Design and conduct a scientific investiga-tion.

(3) Use appropriate tools and techniques to gather, analyze, and interpret data.

(4) Develop descriptions, explanations, pre-dictions, and models using evidence.

(5) Think critically and logically to make the relationships between evidence and expla-nations.

(6) Recognize and analyze alternative expla-nations and predictions.

(7) Communicate scientific procedures and explanations.

(8) Use mathematics in all aspects of scientific inquiry.

In each of our Investigations, ASpECTS OF INQUIRY are indicated that relate to these NRC abilities. The numbers in parentheses that follow the various aspects refer directly to the above list. Since there is obviously overlap among the items, the numbers may be used as guidelines.

1pAGE 29OVERVIEWand species. As you move down the list, each category contains fewer and fewer

animals, and the animals in each category have more and more characteristics in common.

BACKGROUND INFORMATION for the TEACHERThe Classification SystemIn order to communicate with each other, scientists all over the world use the same system to classify and name organisms. The basis of this system (the binomial classi-fication system) is the scientific name which consists of two components, the genus and species names.

For animals, the first category, kingdom, encompasses all of the animals known to mankind. As you descend down the list from kingdom to species, each subsequent category contains fewer animals, and the animals in each category have more char-acteristics in common.

To understand where insects fit into the grand scheme of things, it helps to review the classification system. The animal kingdom is divided into phyla, broad categories that group together animals that have important structural characteristics in com-mon. Insects are animals that belong to the Phylum Arthropoda. The arthropods are all invertebrates (animals without backbones) with a hard outer skeleton called the exoskeleton, a segmented body, and paired jointed legs. Arthropods are further divided into classes, one of which is the Class Insecta. Insects have body segments grouped into three regions (head, thorax, abdomen), three pairs of legs, one pair of antennae, and one or two pairs of wings in most adults.

A NOTE ON THE BACKGROUND INFORMATIONThe background information section at the beginning of each Investigation is for you, the teacher. Here you will find a brief overview of the main concepts of the suite of lessons that follows. The intent is to give you a quick review to help you focus on the important new ideas you will be introducing to students.

Avoid the temptation to share the background information directly with students. Instead, use the information to guide students in discussions and to lead them to their own discoveries and conclusions. In addition, it is very helpful to provide students with other resources such as books, posters, field guides, and periodicals which they may use indepen-dently to further their understanding.

THE LANGUAGE OF SCIENCESince the background sections are addressed to the teacher, they are written in adult lan-guage. The highlighted vocabulary is defined for you as a quick reference tool.

Some of the vocabulary in the background sec-tions is intended to enhance your own learning experience, and is not necessarily appropriate for students. Be selective. You know your own students best.

It is important that students make the lan-guage of science their own, and that they derive their own understanding of new terms. Your goal is to lead students to develop work-ing definitions of the new terms. This process is more effective than simply handing out a vocabulary list. As a result of their efforts, students will begin to incorporate the new terms into their discussions and explanations in an appropriate and meaningful way, and will make the language of science part of their personal vocabulary.

KINGDOM - Animalia PHYLUM - Arthropoda CLASS - Insecta

1 pAGE 30OVERVIEW When Is An Arthropod Not An Insect?

All insects are arthropods, but not all arthropods are insects. Members of several other classes of arthropods are often confused with insects. These include centipedes, millipedes, crustaceans (crabs, lobsters, shrimp, pillbugs) spiders, mites, ticks, scor-pions, and horseshoe crabs.

Although all arthropods have exoskeletons and paired jointed legs, only insects display all of the following characteristics: three body regions, three pairs of legs, one pair of antennae, and one or two pairs of wings. (Note: some adult insects are wingless.) If you encounter an animal with only one or two (but not all) of these characteristics, then it is probably not an insect.

For example, spiders have eight legs, no antennae, and only two body segments. Horseshoe crabs have two body segments and five pairs of walking legs. The crus-taceans, which live mostly in water and breathe through gills, have two pairs of antennae and five or more pairs of legs. Millipedes and centipedes have many body segments, and many pairs of legs, although not the hundreds or thousands that their names imply.

Insects: Numbers and KindsAny description of insects is bound to include superlatives, for they are the most biologically successful and the most numerous animals on earth. Insects outnum-ber all other species of animals combined, and they account for at least 75% of all animals living today.

Entomologists estimate that there are more than a million known species of insects, and perhaps at least an equal number yet to be discovered. When we compare that to the 4,000 or so species of mammals, we can begin to appreciate how diverse insects really are.

WHY LATIN?In the system of classification that has been adopted worldwide, organisms are given Latin or Latinized names. Latin is the root language for scientific naming. Since it is an ancient language no longer in use, it is no longer changing. It also has the advantage of being a neutral language belonging to no modern country or culture.

Common names can be misleading or confus-ing. For example, the shiny black beetle called the bessbug by some may also be known as the patent leather beetle, the betsy beetle, and the horned passalus beetle. But once it is referred to as Popilius disjunctus (genus and species), scientists throughout the world know that they are all talking about the same insect.

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WORD BANKEntomologist – A scientist who studies insects.

Exoskeleton – Arthropods lack an internal skeleton. Instead they have a hard outer cov-ering called an exoskeleton. In these spineless animals, the exoskeleton is secreted by a layer beneath the skin called the epidermis. It is soft at first, but then hardens to form a rigid, protective layer. The exoskeleton is often made up of plates joined by narrow, flexible membranes. In order to grow, the animal must molt (or shed its exoskeleton), and replace it with a larger one.

Invertebrates – Animals with no spinal col-umn or backbone. They are represented by 20 different phyla, the largest of which is Arthropoda.

phylum Arthropoda (from the Greek roots arthro, meaning joint and pod, meaning foot) – A division of the animal kingdom that includes organisms with pairs of jointed legs, an exoskeleton, and a segmented body. Arthropods are the most widely distributed, the most diverse, and the most abundant ani-mals on earth.

Please note that there are also internal ana-tomical structures that differentiate the arthropods from other phyla, but this unit asks students to focus on observable, exter-nal features.

Insect diversity is truly remarkable. Insects inhabit all regions of the globe – from tundra to tropics – although few inhabit the sea. They come in a vast array of col-ors and shapes. For example, contrast the round, brightly-colored ladybird beetle with the elongated and well-camouflaged walking stick; or the huge iridescent blue morpho butterfly with the inconspicuous, wingless flea.

Insects also vary in their modes of locomotion. Depending on the species, they may have body parts that enable them to crawl, walk, hop, fly, dig, or swim.

Their mouthparts are often highly specialized and provide clues to what the insect eats. For example, leaf eaters such as grasshoppers have chewing mouthparts; insects such as butterflies that consume liquids have straw-like, sucking mouthparts; blood-feeding insects such as lice and mosquitoes have piercing-sucking mouthparts.

Grasshopper(chewing

mouthparts)

Butterfly(sucking

mouthparts)

Mosquito(piercing & sucking

mouthparts)

1 pAGE 32OVERVIEW Characteristics of the Class Insecta

Insects are a class of arthropods that share certain distinguishing characteristics that, taken together, set them apart from all other creatures. The most important of these characteristics are:• Like all arthropods, insects have an exoskeleton. This hard, rigid outer covering

provides support and protection for the soft internal organs. The exoskeleton is jointed, divided into segments that are connected by flexible membranes.

• An insect has three distinct body regions: the head, the thorax, and the abdomen.• Insects are hexapods. That is, when an insect has legs, they will be six in number.

These attach to the thorax.• Those insects that have wings usually have two pairs. The exceptions include the

flies, which only have one pair of wings. Wings are attached to the thorax.• All insects have one pair of antennae on the head.

KEY TO INSECT ANATOMY1. Head2. Thorax3. Abdomen4. Legs5. Wings6. Mouthparts7. Antennae8. Eyes

1pAGE 33OVERVIEWAn Insect’s Body Plan

No matter what their color, size, or shape adult insects typically have three distinct body regions: head, thorax, and abdomen.

• HeadAn insect’s head is made up of several plates that are fused together. It bears the sensory organs: a pair of segmented antennae which the insect uses to touch, taste, and smell; and between one and three simple eyes and two larger, compound eyes.

The head also holds the mouthparts which vary widely depending on the species, but generally they fall into one of several categories: chewing, sucking, piercing, sponging, lapping, or a combination of these types. Many insects are highly spe-cialized in their eating behaviors, and this results in a high degree of specialization in mouthparts.

• ThoraxThe thorax consists of three segments. Each segment bears a pair of jointed legs. The wings are attached to the upper side of the second and third segments of the thorax. As you might expect, there are strong muscles inside the thorax that power the animal’s legs and wings.

• AbdomenThe abdomen is also segmented, and is slightly more flexible than the rest of the insect’s body. Soft membranes join the upper and lower plates of each segment and allow the abdomen to expand somewhat. This little bit of flexibility is important. It allows the abdomen to expand and contract during breathing, makes room for developing eggs in the female, and provides space for food that the insect ingests. In some adult insects, the genitalia are visible at the end of the abdomen.

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Place in the EcosystemTo many a human eye, insects are an alien life form, creepy-crawlers that invade our homes and gardens, threaten our crops, spread disease, inflict painful stings or bites, and buzz about in an annoying way. While it is true that a small proportion of insects are destructive or harmful, the vast majority are beneficial.

Insects are an important part of the food chain. Many birds, fish, reptiles, and small mammals depend on insects for their source of energy, and devour them in great quantities.

Without insects, there would be no honey, shellac, or silk. Blossoms would go unpollinated, so fruits and seeds would not develop. Without the work of scavenger insects, dead wood, dung, and carcasses would pile up in great heaps.

Insects are intricately woven into the web of life. It would be impossible to imagine the world without these often beautiful and always intriguing, complex creatures.

ENTOMOPHOBIAIt’s important to recognize that students’ atti-tudes towards insects will vary widely, and that some individuals may even be fearful or repulsed. Negative attitudes often spring from lack of exposure, and it is hoped that the non-threatening experiences with insects provided in the unit will help to dispel some of the fears and aversions that students may harbor.

1pAGE 35OVERVIEW

Darkling BeetleSpecimen Slide

MillipedeSpecimen Slide

pillbugSpecimen Slide

DARKLING BEETLE:Kingdom Animaliaphylum ArthropodaClass InsectaOrder ColeopteraFamily Tenebrionidae

MILLIPEDE:Kingdom Animaliaphylum ArthropodaClass DiplopodaOrder SpirostreptidaFamily Spirostreptidae

PILLBUG:Kingdom Animaliaphylum ArthropodaClass CrustaceaOrder IsopodaFamily Armadillidiidae

Lesson 1: What is an Arthropod?

RECOMMENDED TIME: 2 Class Sessions

MATERIALSJournals16 Hand lenses5 Millipede specimen slides5 Darkling beetle specimen slides5 Pillbug specimen slides*Chart paper and markers*Resource materials, including a dictionary and an encyclopedia, tradebooks and textbooks, field guides, and posters*Microscopes, if available*Rulers*Teacher Provides These iTems

GETTING READY1. Students may want to look up information about terms such as kingdom, phy-lum, arthropod, and insect. Provide a good dictionary and/or an encyclopedia as well

THE LESSON AT A GLANCEStudents:• Discuss classification.• Examine specimens of arthropods to look for characteristics they have in

common. Record data.• Develop a working definition of the term arthropod.• Classify the Backyard Invertebrate Cards; sort for arthropods.

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as other appropriate resources for this activity.

2. Try to obtain one or more microscopes for students to use throughout the unit. Many identifications and analyses are based on very small visual characteristics. This is a good opportunity to practice using the microscope, and to practice making drawings from images seen through the lenses.

3. On the board or on a piece of chart paper, write out the following diagram in the traditional step-wise fashion:

Kingdom Phylum Class Order Family Genus Species

THE INVESTIGATION1. Let students know that they are about to begin a study of insects that will include many different topics, such as insect anatomy, life cycles, and the structures insects build. But first, it is important to review how insects

are classified and to figure out where they fit in the world of animals. Open a brief discussion on the classification system by focusing attention on the chart you have prepared. Ask:

• What does this diagram represent? (Students will probably recognize that it repre-sents the classification system.)

HOW ARE HUMANS CLASSIFIED?Kingdom Animaliaphylum ChordataSubphylum VertebrataClass MammaliaOrder PrimateFamily HominidaeGenus HomoSpecies sapiens

DISCUSSION

Discuss classification.

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Then fill in the first three categories as follows:

Kingdom Animalia Phylum Arthropoda Class InsectaNow ask:• There are two languages used in the classification system. One is English. Do you

recognize the other one? (Students may or may not know it is Latin.)• Why do you think scientists use Latin names for organisms? How does it help

them communicate with each other?• Look at the word Animalia, which is pretty obvious. We are going to be studying

animals. But what does Arthropoda mean? How could you find out?• How does Class Insecta relate to Phylum Arthropoda? Are insects a smaller or a

larger category of animals? Note: Keep the chart posted. Students will later add their definitions of arthropod and insect.

2. Divide the class into five teams. Distribute the preserved arthropod specimens, hand lenses, and measuring tools. Ask students to draw and la-bel the three specimens, and to record their observations in their journals.

Their objective is to search for observable similarities, the attributes that arthro-pods have in common. These will give us clues about why they are classified in the same phylum.

JOURNAL PROMPT• On the blank page, draw each arthropod. Label as many of its parts as you can. Take

measurements and record them on the drawing.• On the lined page, write a brief description of each animal. • What do all three animals have in common? What characteristics make them arthropods?

Examine specimens of arthropods to look for characteristics they have in

common. Record data.

JOURNAL

MANAGEMENT TIPWhenever journal prompts are provided, they are intended as suggestions and guidelines. Feel free to modify the prompts to suit your own students. To help students focus, provide a visual display of the prompts, perhaps on the board, an overhead, or on chart paper.

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As students work, encourage them to use the microscopes (if available). When they have completed their observations, allow them to use the resources you have pro-vided, such as dictionaries and encyclopedias, tradebooks, texts, and field guides.

3. When students have completed their observations, hold a discussion on their findings. Ask:• How are these three organisms alike? What characteristics do they have in

common?• Based on your findings, how would you define the term arthropod? Record stu-

dents’ definitions on the chart, next to Phylum Arthropoda.Note: Students’ definitions should include these elements: An arthropod is an ani-mal without a backbone (spineless animals are also called invertebrates), with a hard outer skeleton (or exoskeleton), a segmented body, and paired jointed legs.• What are the advantages of having an exoskeleton? What does an exoskeleton pro-

vide for the animal?• Are there disadvantages to having an exoskeleton? How does it limit the animal?

THE PURPOSE OF CHECKPOINTSCheckpoints are included as an invitation to the teacher to pause for a moment and consid-er “How are we doing so far?” They are a way for the teacher to think about how the class as a whole is progressing, and to make adjust-ments in teaching or offer coaching. Individual student assessments are provided at the end of Investigations.

Develop a working definition of the term arthropod.

CHECKPOINT: Recording Skills• The three arthropods are difficult objects to draw and require com-

plex written descriptions as well as very fine measurement. Take note of how much effort students expend. Notice whether the de-scriptions are complete and accurate, and whether the drawings are an honest attempt to record what students actually observed.

• Also notice how well students organize their data. It will be impor-tant for them to be able to retrieve and analyze the data in coming lessons.

• Acknowledge that these are difficult tasks, and reassure students that they will improve with practice. Offer coaching to students who seem to be struggling.

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DISCUSSION

4. Distribute the Backyard Invertebrate Cards, one set to each team. Based on the definition they have developed, ask students to sort the Backyard Invertebrate Cards into two or possibly three categories: arthropod, non-arthropod, and (if questions arise) unknown.

Discuss students’ classification and the reasons they sorted the animals the way they did. If possible, have students leave their sorted cards in the two or three piles they constructed so they may return to them later.

5. Revisit the chart and the definitions students developed for the term arthropod. Ask if they want to make any additions, deletions, or corrections to their definitions.

Classify the Backyard Invertebrate Cards; sort for arthropods.

UNKNOWNSStudents may want to establish a category for creatures about which they have questions. It would be useful to record their questions and make them a focus of further research. Students may also find that, as the unit pro-gresses, they will discover their own answers to these questions.

WORMS AND OTHERSThe worm is included for a purpose: to help get out students’ prior knowledge about lar-val stages of insects. Maggots, grubs, and caterpillars are all insect larvae, but are often confused with worms because of their soft, segmented bodies and their sometimes-incon-spicuous legs. Please see Investigation 2 for more complete information on insect larvae. Also see A Guide to Backyard Invertebrates for more information about worms, grubs, mag-gots, and caterpillars.

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CLASS ChART

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Lesson 2: What is an Insect?

RECOMMENDED TIME: 1 or 2 Class Sessions

MATERIALSJournals15 Specimen slides Hand lenses6 Sets of Backyard Invertebrate Cards6 Copies of A Guide to Backyard Invertebrates1 Poster called Insect Anatomy6 Copies of Peterson First Guide to Insects*Chart (from Lesson 1) and markers*Teacher Provides These iTems

GETTING READY1. Display the chart from Lesson 1 on which you have recorded students’ defini-tions of the term arthropod.

2. Hang up the poster called Insect Anatomy.

THE LESSON AT A GLANCEStudents:• Share prior knowledge about the characteristics that define insects. • Use a poster to review insect anatomy.• Reclassify the Backyard Invertebrate Cards; sort for insects.• Read for more information.

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THE INVESTIGATION1. Review the chart on which students recorded their definitions of the term arthropod. Then move to the next category, Class In-secta, and ask:

• What characteristics did you find that members of the Phylum Arthropoda have in common? (pairs of jointed legs, a segmented body, an exoskeleton)

• What do you know about insect characteristics? That is, what additional or par-ticular characteristics do members of the Class Insecta have? (three body regions, six legs, two pairs of wings when they have wings [except for flies], one pair of antennae)

• Which specimen is an insect? How do you know? How is it different from/similar to the other two specimens?

2. Turn attention to the poster called Insect Anatomy and hold a brief review of the structures that define an insect and the functions of each structure. As students respond, add labels to the chart to correspond to each number. For each structure, ask:• What is the name of this part?• What does it do?

At the end of the review, ask students to add their definitions of Class Insecta to the chart.

3. Have students return to the decks of Backyard Invertebrate Cards. Ask them to select the stack that would include Class Insecta. (This would be the arthropod stack.) Then have them reclassify the arthropod stack into two or three categories: insect, non-insect, and unknown. They may also want to revisit their other stacks and add more animals to this new classification. When students have finished sort-ing, ask them to describe the new classification system and explain why they placed animals where they did.

PRIOR KNOWLEDGEStudents will probably have varying degrees of prior knowledge about the characteristics that distinguish the Class Insecta. It is impor-tant to emphasize that insects are members of the Phylum Arthropoda and share all the char-acteristics of those animals, but in addition they have a set of characteristics that, taken together, set them apart from all other classes of animals.

Share prior knowledge about the characteristics that define insects.DISCUSSION

Use a poster to review insect anatomy.

Reclassify the Backyard Invertebrate Cards; sort for insects.

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CLASS ChART

4. Distribute copies of the booklet called A Guide to Backyard Invertebrates and preview it with the class. Go over the introductory information on the first page so students will know how to interpret each subsequent entry. Also distribute the Peterson First Guides to Insects. Then encourage them to do some of the following activities:• Match two of the three specimens to those pictured in the booklet. Match the

third to one pictured in the Peterson First Guide (p. 66). What classes do they be-long to? For the two that are not insects, what unique characteristics help to place them in those classes?

• Check their own classification systems with information given in the booklet. • Look for similarities within the classes of animals. For example, what do arachnids

have in common? • Identify animals they may have seen in your geographical area.

Also let students know that they will be doing a research project at the culmination of the unit. The booklet and field guide may serve as a springboard for ideas and for questions they might research.

MAKING INQUIRY ExPLICIT5. Hold a brief discussion with the class to review the inquiry skills they used in this investigation. Ask:• What have we learned about insects so far? How did we learn it?

Help students define the various inquiry sills they have used: observing, record-ing, comparing and contrasting, discussing, developing a classification system, doing research.• Why are these thinking skills important?

Read for more information.

COLLECTING Students may naturally begin to bring inverte-brates to class, either dead or alive. Encour-age them to use the resources to identify their animals, and then (if living) to provide them with suitable temporary quarters. Please see the Appendix for suggestions on how to treat an insect guest. Limit the time the living crea-tures are kept in captivity to a day or two, and then have students return them to where they were found.

MAKING INQUIRY ExPLICITTo help make the inquiry process more explic-it for students, plan to take a few moments at the end of each investigation to reflect on the skills that they have used to build their knowl-edge base. As students become more aware of the thought processes and inquiry skills they are using in this context, they may be able to apply them to other problems in other content areas.

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DISCUSSION

WHAT HAVE STUDENTS LEARNED?A. What is an arthropod? What is an insect?

B. What is the importance of the classification system? Why is it important for sci-entists to be able to name an organism exactly?

C. To answer questions that we have, we often use ways of investigation that are part of “inquiry,” a process people use to ask and answer questions they are interested in. Choose at least three of the following inquiry skills and give examples of how and when we used them in the first Investigation.• Observing• Measuring• Recording• Comparing and contrasting• Discussing• Communicating findings

ASSESSMENT The assessment questions at the end of an Investigation may address content, process skills, or both content and process skills that students used to gain knowledge.

Students may record their responses in their journals or on a separate sheet of paper.

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