Investigating Hermit Crabs: What
Do They Eat?
Your class has been given a class pet, a hermit crab. You are
unsure of what type of animal it is (carnivore, omnivore,
insectivore or herbivore). Plan an investigation to help you find
out what type of eater it is so you can care for it.
Investigating Hermit Crabs: What Do They Eat?
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Investigating Hermit Crabs: What Do They Eat?
Suggested Grade Span
3–5
Task
Your class has been given a class pet, a hermit crab. You are unsure of what type of animal it is
(carnivore, omnivore, insectivore or herbivore). Plan an investigation to help you find out what
type of eater it is so you can care for it.
Big Ideas and Unifying Concepts
Cause and effect
Interdependence
Systems
Life Science Concepts
Populations and ecosystems
Regulation and behavior
Structure and function
Mathematics Concepts
Data collection, organization and analysis
Graphs, tables and representations
Measurement
Time Required for the Task
45 minutes.
Context
This task comes from a district-wide final science assessment given to third graders at the end
of the school year. During the course of the year, students learned a variety of concepts from
each science strand: physical, earth and life. They also worked on science process skills within
each unit. The entire end-of-year assessment was designed as a means to assess students’
learning from each science strand, as well as an opportunity for students to practice
answering constructed-response test items. This is a skill students will need in fourth and fifth
grades when they will be asked to answer constructed-response items on standardized
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statewide assessments in math, writing and science. This assessment was also developed to
provide the school district with science data about learning, teaching and the science
curriculum. The goal of the school district is to ensure that all students have equal access to
high-quality science instruction and learning.
In the life science strand, students learned about different classifications of animals. They
classified animals as carnivores, herbivores, insectivores or omnivores. Additionally, in all the
science strands throughout the year, students learned and practiced a number of science
process skills such as developing hypotheses; raising questions; making predictions; designing
and conducting investigations; collecting, recording, and analyzing data; drawing conclusions;
and communicating results.
What the Task Accomplishes
This task serves two purposes. First, it will assess students’ understanding of classifications of
animals and how to apply the scientific method to find out what type of eater a hermit crab is.
Second, it will assess students’ understanding of the scientific method and their ability to design
an investigation on their own.
How the Student Will Investigate
This particular task does not ask students to perform an actual investigation. Rather, students
need to apply their understanding of classification and process skills to plan an investigation to
solve a problem. This task could be used during the course of a classification unit in life
science, having students actually conduct their investigation using a class pet, such as a hermit
crab, snail or insect. Precautions would need to be taken to ensure safe and humane treatment
of the animals.
Interdisciplinary Links and Extensions
During the life science strand, many teachers integrated other subject areas, such as reading,
writing, art, math and social studies. Some language arts examples are shared below.
Language Arts
Students wrote and illustrated books about different types of eaters. These could also be done
as A-B-C books or big books for younger children. In one class, they wrote a play to depict the
relationships among different types of eaters in the natural world.
There are many wonderful children’s books that deal with eating habits:
• The Very Hungry Caterpillar, by Eric Carle
• Compost Critters, by Bianca Lavies
• Beastly Neighbors: All About Wild Things in the City, or Why Earwigs Make Good Mothers,
by Mollie Rights
• Stokes Guide to Observing Insect Lives, by Donald Stokes
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Teaching Tips and Guiding Questions
Spend plenty of time reviewing beforehand, especially any difficult vocabulary. Make sure that
students truly understand the terms and conceptual ideas and their relationship to the real
world. For students who do not read on grade level, assistance was given by reading aloud
each question. For students who struggle with writing, the teacher was able to scribe their
answers on the assessment (exactly as dictated by the student).
During the review period, teachers might ask some of the following questions:
•
•
•
•
•
•
•
•
•
What different types of eaters are there?
What are some examples of each?
What things do each of these eat?
What are some ways to learn what type of eater an animal is?
How might you organize and design an investigation to find out?
What steps would you include?
What variables would you control to make it a fair test?
What will you measure? What types of data would you collect?
What tools will you need? What materials will you need?
Concepts to be Assessed
(Unifying concepts/big ideas and science concepts to be assessed using the Exemplars
Science Rubric under the criterion: Science Concepts and Related Content)
Life Science – Structure and Function; Regulation and Behavior; Populations and
Ecosystems: Students identify characteristics of organisms, categorize living organisms as
plant eaters or meat eaters, and classify populations of animals as herbivores, carnivores,
insectivores and omnivores. Students use the terms herbivore, carnivore, insectivore and
omnivore appropriately and are able to demonstrate conceptual understanding, using prior
knowledge.
Mathematics: Students collect, organize and analyze data and use graphs, tables and
representations appropriately. Students use precise measurements.
Skills to be Developed
(Science process skills to be assessed using the Exemplars Science Rubric under the criteria:
Scientific Procedures and Reasoning Strategies and Scientific Communication Using Data)
Scientific Method: Hypothesizing, predicting, planning an investigation, controlling variables,
explaining data, communicating information, making connections between concepts and using
prior knowledge.
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Other Science Standards and Concepts Addressed
Scientific Method: Students hypothesize, predict, plan investigations and control variables.
Students explain phenomena in the living world.
Life Science – Regulation and Behavior: Students understand how plants and animals interact
and behave in order to survive.
Life Science – Populations and Ecosystems: Students understand how to classify populations
of animals based on their feeding patterns.
Life Science – Structure and Function: Students describe and group animals by what they eat
and where they live. Students understand that living things are found almost everywhere in the
world and are interdependent.
Suggested Materials
For this assessment task, students will need only the assessment directions and pencils.
Possible Solutions
Students are asked to make a prediction or hypothesis about what type of eater the hermit crab
is and to then plan a way to test their prediction/hypothesis and include in their procedures what
variables they will control and how they will control them to assure a fair test. They should
identify the types of data they will collect and what the data will then communicate to them.
Students should use appropriate terminology, and their procedures should reflect
understanding of those terms.
Task-Specific Assessment Notes
Novice
This student’s solution is incomplete and lacking in details. The student includes a prediction
but does not use appropriate terminology (herbivore) to describe a plant eater. The student only
names one variable that will be controlled ("crab") and does not include what other specific
foods will be tried, other than salad. The student’s procedure for investigation does not indicate
a clear understanding of classification or scientific process and only begins to indicate briefly
(on a chart) how the data will be collected and analyzed.
Apprentice
The student includes a prediction and uses appropriate terminology. The procedure for
investigating shows some evidence of understanding data collection and includes some
indication of what variables will be controlled (measuring the food). It is not clear what other
specific variables need to be considered, nor are the foods to be tried indicated. The student’s
procedure for investigation does not indicate a clear understanding of classification or scientific
process.
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Practitioner
This student’s solution is complete and begins to indicate an understanding of classification and
scientific process. The student includes a prediction and uses appropriate terminology.
Procedures for investigating show evidence of fair testing in that they include how the student
will control two variables (time given and amounts of food) and what will be used during testing.
The student indicates how the data will be analyzed and the conclusions drawn but does not
connect this with specific classifications.
Expert
This student’s solution is complete and detailed, including a prediction, using appropriate
terminology. The procedure for investigating includes controlling three variables. The student is
very specific about type of food, amount and time of day. The student discusses how data will
be analyzed and connects possible findings with specific classifications. The procedure for
investigation indicates an understanding of classification and scientific process.
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Novice
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Apprentice
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Practitioner
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Expert
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