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Grasshopper & Crayfish Dissection Lesson for Middle School Biology

Updated on May 18, 2019
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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 8.

Arthropod Anatomy & Dissection Lesson for Middle School: Crayfish and Grasshoppers
Arthropod Anatomy & Dissection Lesson for Middle School: Crayfish and Grasshoppers

This is the 26th lesson in a series of 32 hands-on lessons covering middle school biology. This lesson focuses on the study of arthropods through dissections of crayfish and grasshoppers. 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 for students who did their homework and who did the extra credit. Allow students to share what they found interesting or important when studying the crayfish and grasshopper. (I give out tickets for students who volunteer to share their answers.)

Grasshopper Anatomy & Dissection

2. Quickly review about grasshoppers:

  • What do you know about grasshoppers? Has anyone read a book that involved grasshoppers? (Most of the students have read the Little House on the Prairie series that included the grasshopper swarm. Those were Rocky Mountain Grasshoppers, and they are now extinct.)
  • Many cultures around the world enjoy eating grasshoppers. In Mexico they 're called chapulines. They roast them, add chili powder seasoning, and eat them as crunchy snack or toss them in tacos. They're also popular in parts of Africa and Asia. They're high in protein & low in fat. Who would eat one?
  • What phylum are they? (Arthropods, the same as the crayfish)
  • How many body sections do they have? (3 - the head and thorax are separate)

3. External Observation:

  • Since it's an arthropod, it has jointed appendages. Notice the joints: Large jumping legs allow them to jump great distances. The tibia (we also have tibiae) have spines or hooks. Why do you think they have those? They're designed to grab on to vegetation, so the grasshopper doesn’t fall to the ground. Plus, it's a more efficient way to travel on top of the vegetation so it can be more aware of its surroundings.
  • 3 body sections: Head (palps & mandibles with sensory organs), thorax (has legs & wings), abdomen
  • How can we tell if it's a male or female? Look at the tail end. If it has an ovipositor at the end, it's a female. The ovipositor is used to dig holes into soil so she can can lay her eggs. Male of course don’t have one.
  • How many legs does it have? (6). All insects have 6 legs. The hind legs are very broad and very muscular to help it jump. If you had the same jumping power those legs give a grasshopper, you'd be able to jump from one end of a basketball court to the other in one leap. Let's remove those legs. Twist them off (not pull) so you won't damage the internal structures. You can see bits of skeletal muscle at the tips.
  • Did you know grasshoppers have wings? You should be able to find the large, flat dark wings, which are the forewings -"fore" because it's more anterior. How do they feel? (hard & leathery). They're used for gliding & for protecting the smaller wings (hind wings) underneath. Fan out a smaller wing. It's folded up like an accordion and is very thin like a membrane. It's used for flapping & flying & moving up & down. Since it could be easily damaged, it’s protected by the forewings. Gently twist & pull the wings off.
  • Underneath the wings are structures, tympanic membrane or tympanum, which are the grasshopper’s eardrums. They vibrate with sound and how the grasshoppers hear.
  • Just above the lines on the abdomen you should see a pore, one on each segment. Those are spiracles, the entrance ways through which air enters body. Grasshoppers don't have gills like the crayfish or lungs like us. They have spiracles and tracheal tubes, which we'll see after we cut it open. The spiracles ate the introduction of its respiratory system. They don’t breathe through their mouths or skin but through their spiracles.
  • Let's quickly look at the head. What do you notice? They have long antennae, which are sensory, used for tactile/touch and smell/taste reception.
  • Below labrum are large, hard mandibles, which help chew to break down the food. The next pair of appendages are the maxillary palps and labial palps which are sensory for touch, taste, and smell.
  • Grasshopper’s eye is compound and has many lenses called ommatidia, hundreds of them, so it can see more of its surroundings, almost 360 degrees, to see predators.

4. Internal Observation:

  • Starting at the posterior (end), cut up to anterior side. Your blade should be parallel to the exoskeleton to avoid cutting the organs. Cut through the thorax through head region. Be very gentle when opening the exoskeleton and try to only cut in little snips with scissors.
  • What do you notice?
  • If you have a female, you might see lots of eggs & ovaries. We'll need to remove them to see the rest of the internal organs. It's pretty amazing how much space the eggs take up.
  • Can you see there are lots of muscle fiber tissues by the head & neck and the legs, because those are all used for movement.
  • Look for small fibers going from the exoskeleton to body. Those are the tracheal tubes, which are tubes for exchanging gases. They branch & branch & branch & deliver oxygen to all parts of body. You might notice larger ones are near head region.
  • Starting at the mouth we go to the pharynx to the crop.
  • That large balloon-like organ is the crop, which is used for what? Food is stored temporarily before going into what? The gizzard, which is between the crop and stomach. You might also notice digestive glands called gastric caeca. They’re like little flaps of skin and produce digestive enzymes. They're basically the grasshopper's liver.
  • Where the stomach narrows, there are small hair-like structures (they can be difficult to see) called malpighian tubules. They're used to remove metabolic waste. They are like the grasshopper's kidneys.
  • What do you think the smaller tube-line structure is? Yes, the intestine. At the very end you'll find the rectum and anus.
  • Turn it over and you may be able to see the nerve cord, but it's only seen in well-preserved specimens.
  • Spend a few minutes exploring any of the other parts and then clear off your dissection plate and clean up the area.

You will need:

  • grasshoppers (I got one for each group of 4-5 students) - I purchased these preserved from homesciencetools.com
  • dissection kits such as a hard, plastic disposable plate, a paring knife or scalpel, sharp scissors, and tweezers
  • disposable gloves

Crayfish Anatomy & Dissection

5. Quickly review about crayfish:

  • Crayfish are arthropods coming from the same phyla as insects and spiders. Are arthropods vertebrates or invertebrates?
  • All arthropods share some similarities including segmented bodies and hard exoskeletons.
  • Crayfish aren't picky at all and actually make good pets, living in a fresh water tank. They eat about anything and especially love eating dead, decaying fish. They are aquatic, living in the water. They can be found in almost any fresh water source in the United States. Almost all of them are grown (70%) and eaten (90%) in Louisiana.
  • Something neat to note is that they swim backward.

6. External Observation:

  • What do you notice about it?
  • 6 inches long
  • Covered by a hard exoskeleton, like a suit of armor, to protect its soft internal organs. It is similar to a finger nail in that it will flex. It actually has to shed, or molt, as the crayfish gets bigger. What other animals shed their skin?
  • It's divided into segments. Let’s count how many segments it has. (6) The segmented body is characteristic of all arthropods. It's divided into 2 regions: the cephlothroax, which is divided into 2 regions, and the abdomen, which consists of all these smaller sections in the back. Bend the abdomen to see how it moves.
  • You can also see a small indentation line that separates the head (cephalic) from the thorax, but they are not separate. There's just the line.
  • Huge claws called chelipeds. It has 2 that extend to the front of its body.
  • If you flip it over, you'll notice there are quite a few other appendages: several pairs of legs and another pair of feeding arms.
  • Arms are used to eat and pull food to the crayfish's mouth. They're located in between the large chelipid claws.
  • Below that are several pairs of legs. Let’s count the pairs. (Possibly 10. You might have some missing.) They are the walking legs.
  • Below that on the tail are small legs, swimmerets, which are like little paddles or oars, that help it move. It used this entire tail to force water backward, allowing it to swim backward. Female crayfish carry the eggs with their tiny swimmerets.
  • Toward the front at the mouth are 2 white jaws that help predigest the food. When you chew food, how does your mouth move? (Up and down.) The crayfish’s mouth moves from side to side. Using the two large claws, or chelipeds, and two small feeding appendages, or maxillipeds, the crayfish captures its prey, and passes the food to its mouth, where two jaws, or mandibles, crush the food by moving side to side. Notice how the mandibles are hard and difficult to move.
  • It has eyes that project out from its head. The brain is just behind the eyes.
  • It has 2 pairs of antenna. The longer pair is called antenna while the shorter pair are antennules. These are the feelers. What are your five senses? What part of your body do you use for each sense? The long antennae allow the crayfish to touch and taste (and keep its balance). The shorter antennules allow the crayfish to touch, taste, and smell!

7. Internal Observation:

  • Using your scalpel or knife, make 3 cuts through carapace, the top covering. We'll follow the oval shape that's already there. Now use your scissors if it’s easier to remove the exoskeleton near the head area. Remove the covering that goes over body and then head.
  • What do you notice?
  • What do we use to breathe? (noses, mouths, esophagus, lungs) One the sides of the crayfish are feathery things. They are gills, which is how they breathe. Water flows through the gills and releases carbon dioxide picks up oxygen. That’s how they can breathe under the water! Can you think of any other animal that uses gills to breathe? (fish) They are on either side. The crayfish has a strange way of breathing. He just walks! Since his gills are attached to his walking legs, they wave in the water as he walks along! The oxygen is absorbed by the blood vessels in the gills. What a clever Creator the crayfish has!
  • Most organs are found in the center. The largest is the stomach. It's just below the head. Inside the stomach are a second pair of teeth. They help to further digest the food.
  • Looking into the head you can see the brain. It’s right between the eyes. It is a small, white tissue area. Radiating out from it are numerous thread-like structures that are nerves. The nerves mostly run to the eyes and antennae.
  • To the right are green glands or bladders. They excrete waste. The crayfish excretes waste from the front of its body since it swims backward.
  • Going toward the back, you'll find nerves and the intestine. Cut open the tail to see the intestines. On top of the tail is the black line = intestine. Extending from the stomach toward the anus.
  • The tail is the part that is eaten. It is mainly muscle. It would be boiled or steamed. It is very muscular and flexes rapidly, allowing it to swim quickly.
  • Examine the claws: chelipeds. It's similar to a human arm. You have your forearm, wrist, and hand part. Cut just above wrist. If you look down you'll notice the muscles that attach the 2 parts of the pinchers. If you move the claws, you can see the muscles move inside. You might be able to grab the specimen tendons and move the claws to open and close them.
  • Spend a couple minutes exploring any of the other parts and then clear off your dissection plate in preparation for our next specimen.

You will need:

  • crayfish (I got one for each group of 4-5 students) - I purchased these preserved from homesciencetools.com, but you could purchase them fresh if you live in an area that has them available (like Louisiana or Texas)
  • dissection kits such as a hard, plastic disposable plate, a paring knife or scalpel, sharp scissors, and tweezers
  • disposable gloves

Clean up

8. Clean up. Answer any further questions students may have.

A Beka's Science: Order & Design science textbook
A Beka's Science: Order & Design science textbook

Homework

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

  • Friday: Read pp. 363-370. Answer 7 questions of your choice from p. 370.
  • Monday: Read pp. 370-378. Answer 6 questions of your choice from p. 378.
  • Tuesday: Complete the Compare the Anatomy of Arthropods worksheet.
  • Wednesday: Sketch (in color) and identify 5 different arachnids, centipedes, or millipedes that you find outside. (Spiders will probably be the easiest to find and sketch.)
  • Extra Credit #1: Bring in a live (contained) or dead crustacean, arachnid, centipede, or millipede. (If you have capture a live one, make sure it has oxygen. If you capture one for more than a day, make sure it gets food.)
  • Extra Credit #2: Complete the Arthropod Poetry worksheet.

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© 2019 Shannon

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