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Crustaceans & Arachnids Lesson for Middle School Biology

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I am a Christian. I was an 8th-grade American History teacher. I am currently a freelance writer, public speaker, & homeschooling mom of 9.

Middle School biology lesson on arthropods: crustaceans, arachnids, millipedes, and centipedes

Middle School biology lesson on arthropods: crustaceans, arachnids, millipedes, and centipedes

This is the 27th lesson in a series of 32 hands-on lessons covering middle school biology from a Christian perspective. This lesson focuses on the "other" arthropods: crustaceans, arachnids, centipedes, & millipedes! I used this plan while teaching a 55 minute middle school biology class. Each lesson plan includes homework assignments and a variety of hands-on activities to make each lesson engaging & memorable. Use these fun lessons with your classroom, homeschool, after-school program, or co-op!

These lessons are written for a class that meets once a week. If your class meets 5 days a week, simply do this lesson one day a week and use the homework assignments (at the bottom of the page) for the work for the other days of the week.

Homework Review

1. Pass out tickets to students who did their homework and to students who did extra credit. Go over the homework questions from the book. (I give out tickets for students who volunteer to answer the questions.)

2. Ask for students to share about anything interesting they noticed when finding and identifying arachnids, millipedes, or centipedes. (Give tickets to students who share.)

3. If any students brought in live or dead crustaceans, arachnids, millipedes, or centipedes, allow for them to show what they brought when we discuss that class of arthropods.

Venn diagram comparing the classes of arthropods

Venn diagram comparing the classes of arthropods

Crustaceans Overview

3. Give a brief & quick overview of crustaceans while looking at pictures from the textbook or a PowerPoint.

  • How is the exoskeleton of a crustacean different from that of an insect? (Both are made of protein and chitin but the crustacean's exoskeleton also has calcium carbonate, which is the same substance that forms limestone.)
  • Where do most crustaceans live? (Most are aquatic.)
  • Name some crustaceans. (wood lice, barnacles, shrimp, prawns, crayfish, lobsters, crabs)
  • Size range: 1/200 of an inch (water flea) to 24 inches (Tasmanian giant crab)
  • Smaller ones are essential in marine food chains & larger ones are tasty to us (popular seafood)
  • On the unclean list of the dietary law (not to eat) for Israelites
Inspecting barnacle shells

Inspecting barnacle shells

Crustacean Orders: Note-Taking Practice

4. Give a brief overview of the crustacean orders while looking at pictures from the textbook or a PowerPoint.

  • I asked lots of questions and passed out individual M&Ms (or Skittles) to students who answered questions. They are allowed to use their textbooks.
  • Have the students take traditional notes on each order using the below format. I did the first one with them.

I. Crustacean Order

A. Member(s)

B. 1 distinctive trait

C. 1 interesting fact

You will need:

  • (Optional) small candy pieces (M&M's, Skittles, Smarties, etc.)
Crab from the Order Decapoda

Crab from the Order Decapoda

Scroll to Continue

Order Decapoda

I. Decapods

  • "ten feet"
  • Name some members of the Order Decapoda (lobsters, crabs, shrimp, prawns, & crayfish - about half are crabs)
  • Since we covered the anatomy of crayfish, which are in this order, while doing the dissection, you should remember a few of the body parts. What do we call the "armor" for vital organs, which is the extra hard shell covering the cephalothorax? (carapace)
  • What is the forward part of carapace called? It protects the head. (rostrum)
  • What are the front 2 of the 10 legs called? They're used for protection & seizing prey. (chelipeds - crabs & crayfish have large ones but shrimp have very small ones)
  • What are the lower ends of the gills attached to? (legs - so the gills wave through the water as animal moves & since the gills remain moist, some decapods can live for a short time out of water.)
  • Why aren't horseshoe crabs considered to be crabs? (They don’t have feelers.)
  • Does a crab have an abdomen? (Yes. It keeps its abdomen tucked beneath its carapace You must turn it over on its back to see it.)
  • What do you call a newly hatched crab? (Zoeae – They have transparent bodies & very large eyes. They must go through many molts before they appear like adults.)

You can use:

  • If you have a store nearby that carries whole crabs or shrimp (seafood section of the grocery store), the students would enjoy inspecting it. I used to purchase them at the Asian grocery store, but I don't live near one anymore.

Written Notes:

I. Decapoda

A. lobsters, crabs, shrimp, prawns, & crayfish

B. "10 feet"

C. Baby crabs (zoeae) are transparent.

Gammarus roeselii (freshwater shrimp)

Gammarus roeselii (freshwater shrimp)

Order Amphipoda

II. Amphipods

  • “different foot” = 2 types of legs
  • freshwater shrimp & sand fleas
  • first 4 pairs of 14 legs point forward (walking) & last 3 pairs point backward (swimming or jumping)
  • scavengers
  • not true shrimp: eyes not on stalks & no carapace


Order Copepoda

IIII. Copepods

  • "oar-feet"
  • plankton
  • are tiny, less than 1/3 inch
  • no carapace
  • most have a single simple eye on top of its head (so one genus is Cyclops)

Order Branchipoda

IV. Branchipods

  • “gill feet”
  • water flea & brine shrimp
  • water flea has transparent carapace so you can easily see internal organs
  • brine shrimp live in water so salty that many predators can’t survive in such concentrated water; not a true shrimp because has 22 legs rather than 10 & no carapace; dehydrated “eggs” (cysts) can survive for years & hatch when placed in water = Sea Monkeys
  • shortened antennae & leaf-like legs used for swimming or feeding
  • breathe with gills located on feet

You can use:

  • You give away or show a package of Sea Monkeys (sometimes sold at Walmart in the toy aisle) or even show the brine shrimp already hatched

Order Cirripedia

V. Cirripedia

  • "footed one"
  • barnacles - 2 groups by how shells attach: acorn barnacle (attached directly) & gooseneck barnacle (attached by stalk)
  • larva is free-swimming & then attaches itself headfirst when preparing to become an adult
  • hard calcium carbonate shells
  • spend rest of its life using its legs to sweep water that contains food particles toward its mouth
  • most live in shallow water, inter-tidal zone
  • survive low tide by closing shells
  • lots of (biofouling) research has been done to determine how to deter barnacles from attaching to ships, as they can cause serious damage - Some research was done at the University of Florida, studying the skin of sharks and dolphins (which don't have barnacles attach to them) vs. whale skin (which does sometimes have barnacles).

You can use:

  • I passed around some shells with barnacle shells on them.
Northern krill (Meganyctiphanes norvegica)

Northern krill (Meganyctiphanes norvegica)

Order Euphausiacea

VI. Euphausiacea

  • “shining bright”
  • Krill
  • bio-luminescent
  • significant part of marine plankton
  • 1-3 inches
  • have more than 10 legs & no maxillipeds
  • body generally transparent with red patches – in Antarctic plankton numbers are so abundant they make water appear brick red
  • Eaten mainly in SE Asia to make shrimp paste & also used to make krill oil supplements, which are high in omega-3 fatty acids (like fish oil capsules but a lot fishier tasting)

You can use:

  • I have krill capsules & let the students smell them - They can try one if they'd like, though first check for shellfish or fish allergies.

Order Isopodsa

VII. Isopods

  • “equal feet”
  • wood lice (pill bugs or sow bugs)
  • only true terrestrial crustaceans
  • pill bug rolls into a ball when threatened (also called a "roly-poly bug")
  • not an insect because have more than 6 legs
  • all legs are similar
  • breathe with gills so must live in damp places
  • God’s “clean up crew” = eat decaying vegetation

You can use:

  • live pill bugs
Watching a spider kill an insect & passing around a mounted scorpion

Watching a spider kill an insect & passing around a mounted scorpion

Arachnids Mythology & Specimens

5. Summarize the myth of Arachne, while flipping through the pages of a children's book or by showing pictures on PowerPoint.

You will need:

  • a children's picture book retelling of the myth of Arachne (such as Arachne Speaks by Kate Hovey) or pictures on PowerPoint.

6. If students brought in arachnid-related specimens or items, pass them around.

  • The students loved watching a captured spider kill an insect.
  • If you happen to have a black light and a scorpion, it is really neat to see the scorpion glow under the black light.
  • When looking at a spider using a magnifying lens, be sure to note the mouth, eyes, and legs. How many segments can you count on each leg (7). The last segment is surrounded by pad of hairs that helps the spider cling to walls & ceilings.
  • Watch a live spider move. It moves by moving 1st & 3rd legs on 1 side of body together with 2nd & 4th legs on other side.

You will need:

  • arachnid-related specimens or items - I like to bring in a few items just in case no one brings something. Ideas include a dead spider (to see the legs curled up), a live spider captured in a jar with holes punched through the top for air, a tick (inside a jar or dead in a bag), & a scorpion.
  • magnifying lenses (optional)
Arachnid portion of Venn diagram comparing the classes of arthropods

Arachnid portion of Venn diagram comparing the classes of arthropods

Arachnid Notes

7. Compare arachnids to insects and crustaceans by completing the Venn diagram.

  • Similar to crustaceans: 2 body regions; protective carapace; regeneration lost appendages & becomes larger with each molt
  • Different from crustaceans: simple eyes; 4 pairs of walking legs; no antennae, mandibles, or wings; don’t undergo metamorphosis
  • Similar to insects: breathe air rather than through gills

8. Give a brief overview of arachnids while looking at pictures from the textbook or a PowerPoint. Students will not be writing down notes on this information. Again, I asked lots of questions and passed out candy when students answered correctly. They can use their textbooks.

You will need:

  • (Optional) small candy pieces (M&M's, Skittles, Smarties, etc.)

Questions & Notes:

  • What are some orders or arachnids? (spiders, harvestmen, mites, ticks, scorpions, & pseudoscorpions)
  • How are they beneficial to us? (eat lots of insects)
  • What do they use to breathe? (book lungs - respiratory structure made of thin, flat folds of tissue arranged like pages of a book; air enters through spiracles & lungs “pages” (lamellae) exchange oxygen with carbon dioxide)
  • They're covered in lots of bristle-like hairs which serve as organs of touch, hearing, & smell. What do we call those? (setae) Which animal did we dissect that also had setae? (worm)
  • Tell me something special about their mouths. (1. Most have sucking mouth parts instead of chewing. 2. Chelicera – between eyes are fangs/chelae used for seizing & crushing prey 3. Pedipalps – assist in guiding food toward arachnid’s mouth + organs of smell & touch 4. Both chelicera & pedipalps = tools for digging & weapons to defend against enemy)

I. Spiders

  • 2 groups: true spiders (side-to-side movement of chelicerae; most live less than a year)...What is the 2nd group called? (mygalomorphs) What makes mygalomorphs different from true spiders? (chelicerae moves up & down; live up to 20 years) Name a mygalomorph. (tarantula)
  • How many eyes do most spiders have? (8 simple eyes - Most can only perceive movement; wolf & jumping spiders have good eyesight. Researchers put spiders in a room with a TV screen showing other spiders and insects. Most spiders didn't pay attention to the TV, but the wolf & jumping spiders did watch the TV closely when it saw a potential mate or potential food on the screen.)
  • If most spiders can't see well, how do they know something has landed on her web? (sense of touch (setae) & feels vibrations)
Spider web activity: feeling vibrations

Spider web activity: feeling vibrations

Spider Web Activity: Feeling Vibrations

9. Allow students to feel vibrations on a "web." This should not take much time.

  • Divide students into groups of 4.
  • 1 person in each group will get a turn closing their eyes and placing 2 fingers gently on a piece of yarn or string that has been tied between 2 objects (like 2 chairs).
  • One of the other students in the group with tug on the piece of string lightly and with more force.
  • Allow for each student to have a turn doing both roles.

You will need:

  • yarn or string attached 2 two items (like table legs or two chairs) with the yarn pulled taunt - You'll need 1 "station" for every group of 4 students
Arizona bark scorpion (Centruroides sculpturatus) glowing under ultraviolet light.

Arizona bark scorpion (Centruroides sculpturatus) glowing under ultraviolet light.

Arachnid Notes Continued

10. Continue with a brief overview of arachnids while looking at pictures from the textbook or a PowerPoint. Again, I asked lots of questions and passed out candy when students answered correctly.

  • Do spiders chew their food? (No, they can’t chew food, so they spray or inject their meal with enzyme-containing digestive juices from fangs = dissolve insides = suck up insides like a tasty soup)
  • Since spiders don't have muscles to move their legs, what does cause them to move? (Blood pressure -- so when blood pressure drops because of lack of fluids, legs draw up under its body. That's why dead spiders have their legs pulled up.)
  • How many spinnerets does a spider have? (6 - At rear of abdomen - Silk is in liquid form & transformed into stretchy threads when passes through spinnerets. Some silk is 5x stronger than steel cable of same size.)
  • What are some of the different types of silk a spider produces? (for wrapping prey, making webs, forming egg sacs)
  • What are the two venomous spiders we need to avoid around here? (brown recluse & black widow)
  • What is the most dangerous spider in the world? (funnel-web spiders mostly in Australia)
  • What is the largest spider in the world? (Goliath bird-eating spider (Theraphosa blondi) from Venezuela & Brazil - It's leg-span can grow to 11 inches, which is the size of a dinner plate.)

II. Harvestmen

  • Why aren't harvestmen/"daddy longlegs” classified as spiders? (only 2 eyes; lacks constriction (“waist” between 2 body regions, so only 1 body); no spinnerets; no book lungs – breathe using spiracles & trachea)
  • Who has ever caught a harvestmen/"daddy longlegs”? It can lose all by which legs? (both of 2nd pair of legs) Why? (It's sense organs are on 2nd pair of legs.)
  • What's another way they protect themselves from predators? (releases a foul-smelling odor)

III. Scorpions

  • Who has been stung by a scorpion? The stings from the ones around here usually just feel like a bee sting.
  • There's usually a correlation between how large the chelae/pinchers are & how venomous it is. The ones with larger chelae are usually less venomous.
  • All scorpions are venomous but most aren't lethal to humans. Of the 1,750 species, only 25 are lethal to humans. The Arizona bark scorpion (Centruroides exilicauda) is the most venomous in the US. It's sting can kill young children & some people with compromised immune systems.
  • one of few animals that light glow under black light (other animals include flying squirrels, some opossums, puffin beaks, & some marine life)
  • last segment (telson) has venomous stinger & usually only stings large or very active prey
  • no trachea; breathes only through book lungs
  • don’t lay eggs; give birth to live young & cling to mother’s tiny chelae until first molt

IV. Pseudoscorpions

  • How are pseudoscorpions different from scorpions? (They have short, flat abdomen & no stingers but do have poison glands at tips of chelae to kill small insects)
  • Usually grow no more than 1/5 an inch so not dangerous to humans
  • seldom seen because usually live under leaves, loose bark, or pages of books (book scorpions)
  • like spiders they have silk glands from opening on chelicerae to build cocoon for winter months

V. Parasites: Mites & Ticks

  • 45,000 species (possibly 1 million unidentified ones)
  • usually mites are smaller
  • How are they like harvestmen? (have no constriction - just 1 body part)
  • What are some diseases you can get from ticks? (Rocky Mountain Spotted fever (wood tick), Lyme disease (deer tick), & Texas fever (cattle tick))
  • What are some diseases you can get from mites? (scabies & mange)
  • What is a chigger or "red bug"? (larval form of harvest mite & can cause dermatitis)
Holding a millipede

Holding a millipede

Many-legged Arthropods

11. Give a brief overview of centipedes and millipedes while looking at pictures from the textbook or a PowerPoint. I asked questions and passed out candy when students answered correctly. They can use their textbooks.

You will need:

  • (Optional) small candy pieces (M&M's, Skittles, Smarties, etc.)

Questions & Notes:

I. Class Chilopoda - Centipedes = “hundred-footed”

  • Are they carnivores, herbivores, or omnivores? (Carnivores - The usually don't bite humans but they can.)
  • What do they mainly eat? (cockroaches & silverfish)
  • All appendages except for their first pair (maxillipeds) are for what? (walking = quick)

II. Class Diplopoda – Millipedes = “thousand-footed”

  • Are they carnivores, herbivores, or omnivores? (herbivores)
  • Are they faster or slower than centipedes? (Slower - It glides slowly so it can’t escape a predator. Instead it has stink glands or coils into ball.)
  • How are they helpful to us? (eats decaying plants)

Discuss Homework Assignments

Before students leave, quickly discuss the homework assignment for Friday (as it needs to be started on Friday) and the extra credit homework assignment on the Algae Scavenger Hunt. Also mention a few options for the extra credit homework assignment regarding creating a 3-D model of a cell.

A Beka's Science: Order & Design science textbook

A Beka's Science: Order & Design science textbook


(Page numbers refer to the pages in A Beka's Science: Order & Design textbook.)

  • Friday: Complete Check it Out on pp. 393-394. *You will need to start this on Friday...or even today!* Simply draw what you see using a magnifying lens if you do not have a microscope. If possible, bring your moldy food to class (in a closed container like a ziplock baggie).
  • Monday: Read pp. 380-386, skipping Check it Out on pp. 383-385 and pp. 386-387. Answer 6 questions of your choice from p. 387.
  • Tuesday: Read pp. 388-395, skipping Check it Out on pp. 389, 393-394, 395-396. Answer 7 questions of your choice from p. 396.
  • Wednesday: Sketch and identify 4 different types of mushrooms or bracket fungi you find outside. For an extra ticket, sketch and identify an additional 4 more. (Please do not eat or taste the mushrooms that you find!) *Also, don't forget to bring your moldy bread and cheese to class tomorrow!
  • Extra Credit #1: Algae Scavenger Hunt: List as many products as you can that contain algae, including seaweed. (Look for alginate, agar, and carrageenan in the ingredients). These items must be ones that you have actually held in your hand. (i.e. Do not simply look up a list on-line.) Multiple flavors of the same item will not count as separate products. The person with the most products listed will get an extra ticket and an additional prize.
  • Extra Credit #2: Create a 3-D version of a cell. Label your parts (if possible) or write a list of what each part represents. Directions can be found at . (You will need to cut and paste the link.)
  • Extra Credit #3: Complete the Animal Cell and Plant Cell worksheets (printed on a front and back page)

© 2019 Shannon

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