Children will compare crustaceans to insects and experiment with salt water.


Lesson Objective

Children will compare crustaceans to insects, learn about their dependence on salt water, and experiment with saltwater.


What You'll Need

  • Pictures of a variety of insects (ladybugs, crickets, caterpillars, ants, etc.)
  • Pictures of a variety of crustaceans (hard-shell crab, horseshoe crab, hermit crab, lobster, crayfish, shrimp)
  • Warm water – 2 cups per partnership
  • Measuring cups – 1 per table
  • Clear plastic cups – 2 per partnership
  • Salt – 6 tablespoons per partnership
  • Eggs – 2 per partnership
  • Plastic spoons – 1 per child

What To Do

Note: Assign each child a partner to work with to perform the experiment. For each partnership, mark one of the cups with an “S” to indicate the cup containing the salt water.

  1. Display the pictures of the insects and crustaceans. Begin a discussion with the children about how these animals are alike and how they are different (see Did You Know?).
  2. Continue the conversation with the children, leading up to where these animals live (see Did You Know?).
  3. Tell the children they will be performing an experiment to see if there is a difference between salt water and fresh water by floating eggs in both salt water and fresh water.
  4. Distribute the cups, salt, and spoons to the children.
  5. Measure 1 cup of warm water, and pour into each of two cups per partnership.
  6. Have partners take turns stirring the salt into the “S” cup of water until it dissolves.
  7. Demonstrate carefully lowering an egg into the fresh water with the spoon. Repeat by lowering the other egg into the salt water.
  8. Distribute the eggs, and assist the children as necessary with carefully lowering the eggs into the water.
  9. Observe the eggs in the cups of water, and discuss (see Guiding Student Inquiry).

Guiding Student Inquiry

  • Explain how you know that a crustacean is not an insect.
  • Tell me something that is the same about the insects and the crustaceans.
  • Tell me what is different about them.
  • Tell me which kind of animal needs salt water to live.
  • Explain the difference between the two cups of water.
  • Describe what happened to the eggs.

Explore, Extend & Integrate

  • You can extend this experiment to suspend the egg between the fresh water and the salt water. Very carefully pour the fresh water on top of the salt water, taking care not to disturb the salt water. Do not mix the water. Slowly, without disturbing the water, lower the egg into the water. The egg will be suspended in the middle because it will sink through the fresh water but float on the salt water.
  • Transform your sand table into a “mini-shoreline” by adding shells, pebbles, plastic fish, and sea creatures. Leaves from silk flowers make great seaweed! Add magnifying glasses and sifters for greater exploration.

Check for Children’s Understanding

  • Could children describe the difference between the insects and crustaceans?
  • Could children explain that salt water animals need salt water to live?
  • Could children explain the difference between the two cups of water?
  • Could children describe how the eggs reacted in the water?


Did You Know?

Crustaceans and insects are groups of animals that belong to a much larger group of animals called arthropods. Arthropods are animals that have segmented bodies, jointed legs, and a hard shell called an exoskeleton. Crustaceans, like insects, move from place to place by crawling; however, some crustaceans can swim. Crustaceans have 10 or more legs; insects have 6. Insects live all over the world in soil, trees, and water. Crustaceans usually live in or near the water. Most crustaceans that live in the water live in salt water. For instance, lobsters, crabs, and shrimp are found in the ocean. A few crustaceans, such as crayfish, live in fresh water. Fewer still, like wood lice, live on land. The largest and the smallest arthropods in the world are crustaceans.

Ocean water has a high concentration of salt in it, which makes it have more density than fresh water. Fresh water comes from rain and snow and is free from dissolved salt. Salt water is in oceans and seas and contains salt from millions of years ago that cannot escape. While fresh water evaporates, the salt in salt water stays in the water. Animals that live in salt water need salt water for food, stages of their development, and shelter. Although they need salt water for their survival, these animals have a special way of eliminating the excess salt from their bodies.

Vocabulary: Child-Friendly Definitions

  • crustacean – an animal with a hard, jointed shell; crustaceans are a kind of arthropod.
  • insect – a small animal with a three body parts, two antennae, six legs, and a hard covering over its body.
  • arthropod – a large group of animals with hard shells on the outsides of their bodies, legs with joints, and no bones inside their bodies.
  • salt water – water that is full of salt.
  • fresh water – water that is not salty.
  • density – the state of having parts very close together with very little space between.

Lesson Tips

  • Be sure to mark one of the cups with a sticker or an “S” to indicate which cup contains the salt.
  • Be sure to use fresh eggs in the experiment. Older eggs will float in tap water because their density changes as they age.
  • You might want to create a Venn diagram to clarify the comparison of crustaceans and insects.


  • About Crustaceans: A Guide for Children by Cathryn Sill
  • Into the A.B. Sea: An Ocean Alphabet Book by Deborah Lee Rose
  • 10 Little Hermit Crabs by Lee Fox
  • Crabs Are Crustaceans by Cindy Vining

Home School Resources

Home educators: use these printable lesson PDFs to teach this lesson to your home schoolers. They're available in English and Spanish.

Home/School Connections

Las Conexiones a la Casa

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Content Provided By

Common Core State Standards Initiative – These lessons are aligned with the Common Core State Standards ("CCSS"). The CCSS provide a consistent, clear understanding of the concepts and skills children are expected to learn and guide teachers to provide their students with opportunities to gain these important skills and foundational knowledge [1]. Visit the CCSS