Worksheet

Green or Brown? Beetles on the Rail Trail

Grade 8 natural selection practice: use clay-model and beetle survey data to explain how inherited color helps some beetles survive and reproduce.

Grade 8ScienceInteractive · Printable

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1 NGSS standard
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10 questions
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Format: Interactive · Printable
Grade: Grade 8
Subject: Science
Question types: Fill in the blank, Multiple choice, Sorting, Short answer

About this worksheet

What students practice

Students use predator data to explain how an inherited trait affects survival in different seasons.
Students explain why individuals with a helpful trait tend to leave more offspring.

How to use

Read the passage and name the variables of the clay-model test as a class, then let students work through the data and write the explanation on their own.

Curriculum

NGSS standard covered

MS-LS4-4

Explain how genetic variation in traits makes some individuals more likely to survive and reproduce.

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Green or Brown? Beetles on the Rail Trail

Use predator data to explain how inherited color variation affects survival and reproduction.

Part 1: The clay beetle test

Read the passage and the graph, then answer the questions.

Color in the Meadow

1An old railroad line on the edge of town was turned into a walking and biking trail, and the strip of meadow beside it is now a county nature area. Keziah Morrow, an eighth grader, joined the county's summer science volunteers there. Their project was a small leaf beetle that lives on the meadow grass. In this population, some adult beetles are bright green and others are tan-brown.

2The county biologist explained that body color in this beetle is an inherited trait. In the county lab, pairs of brown beetles mostly had brown offspring, and pairs of green beetles mostly had green offspring. The lab also kept 40 adults in clear containers for their whole adult lives, and none of them changed color. Adults appear in late spring, feed on grass all summer and lay eggs on the ground in October. Females of both colors laid about the same number of eggs in the lab. The eggs hatch the next spring.

3The meadow changes with the seasons. In June the grass is fresh and green. By September, after the hot, dry weeks of late summer, most of it has turned tan. Songbirds such as sparrows hunt in the meadow and find insects mainly by sight.

4To test whether color affects how often birds attack the beetles, the volunteers made 100 clay models of beetles, all the same size and shape. They painted 50 green and 50 brown and pinned them to grass stems at evenly spaced spots across the meadow. After 3 days they counted the models with beak marks. They repeated the test with 100 fresh models in September, in the same spots and for the same number of days. The volunteers wore gloves when handling the clay and recorded results on a shared data sheet so each model was counted only once.

5The volunteers also counted live beetles in the same 20 sample plots twice. In early June they found 60 green and 40 brown beetles. In early October, just before egg laying, they found 18 green and 32 brown beetles. Keziah noticed that no new adults appear between June and October, so every beetle in the October count had survived the whole summer.

Which was a controlled variable in the clay model test?

A. The color the models were painted
B. The size and shape of the models
C. The number of models with beak marks
D. The color of the meadow grass

Use the graph. 50 green models were put out in June.

What percent of the green models were attacked in June? %

Use the graph. 50 brown models were put out in September.

What percent of the brown models were attacked in September? %

What do the results suggest about how safe each color is in each month?

A. Green is safer in June and brown in September, matching the grass color.
B. Brown is safer in both months, since birds attacked 25 brown models in all.
C. The colors are about equally safe, since 28 green and 25 brown were hit.
D. Green is safer in both months, since birds tend to avoid bright colors.

Part 2: Surviving to lay eggs

Use the passage, the graph and the beetle counts in paragraph 5.

Use the June and October counts for each color.

Percent of green beetles that survived to October: %
Percent of brown beetles that survived to October: %

Sort each difference between beetles by whether it can be passed to offspring.

Green or brown body colorA chipped wing cover from a bird's beakDust coating its back after a dry weekLonger legs, like both of its parents

Inherited variation	Not inherited

A volunteer says green beetles turn brown in late summer so they can hide on the tan grass. Which evidence from the page best shows this is wrong?

A. Birds attacked 21 green models in September.
B. More green beetles than brown beetles were found in June.
C. The lab beetles turned brown when their grass dried out.
D. The lab beetles kept the same color all their adult lives.

What would you predict about the young beetles that hatch next spring?

A. They will be mostly green, since green is safer when they hatch.
B. Each one will pick its color to match the grass as it grows.
C. A larger share will likely be brown, since more brown parents survived.
D. About 60 out of every 100 will be green, the same as this June.

Use the beetle counts in paragraph 5.

How many more brown beetles than green beetles were alive in October? beetles

10.

Explain how variation in body color affects which beetles in this meadow survive and reproduce. Write a claim, use at least two numbers from the page as evidence and explain your reasoning.