Updated 2026-08-23easy

TOEFL Reading Practice #002 — The Grasshopper That Becomes a Locust

Free TOEFL Reading practice: The Grasshopper That Becomes a Locust. 11 questions with a full passage and answer key.

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How to use this practice: Read the passage once without a dictionary, then answer the questions on your own. Tap “Answer” under each question to reveal just the correct letter — no explanations, so you can keep testing yourself.
1

Passage

Read the full passage. Bracketed letters like [A] mark the four positions for the insert-text question.

The Grasshopper That Becomes a Locust

¶1 A single locust swarm can hold more than forty million insects in one square kilometer. That many locusts can eat as much food in a single day as thirty-five thousand people. Yet nearly every locust begins life as an ordinary grasshopper. It is a quiet insect that lives alone and eats very little. Something turns that calm insect into part of a hungry, traveling crowd.

¶2 Researchers have identified the trigger: touch. When heavy rain brings fresh plants, grasshoppers gather in large numbers. Their back legs keep brushing against each other. Because this touching happens again and again, the level of a chemical called serotonin rises sharply within a few hours. That sharp rise flips a switch inside the insect's body. Its color turns darker, its wings grow longer, and it stops avoiding other grasshoppers. Scientists call this shift a phase change. The insect moves from a shy, solitary phase into a bold, gregarious phase.

¶3 Once enough grasshoppers switch phases, the real trouble starts. [A] Gregarious insects do not scatter the way solitary insects do. Instead, they gather into marching bands that stay close together. [B] The bands grow larger as more insects join and switch phases along the way. Sometimes the bands stretch for many kilometers. [C] After several weeks, the young insects grow wings and lift off together. The flying swarm they form can cross more than a hundred kilometers in a single day. [D] The swarm keeps growing because every new landing spot brings fresh plants and more crowding. That crowding causes even more insects to switch phases.

¶4 This process struck East Africa in 2020. It was the worst locust outbreak the region had faced in decades. Unusually heavy rains created perfect breeding grounds, and locust numbers exploded within months. Some swarms grew large enough to cover an area the size of a major city. Farmers watched entire fields disappear within hours. The outbreak put food at risk for more than twenty million people across the region. In the end, the disaster began with nothing more than crowded insects touching each other's legs.

  • locust: a type of grasshopper that can gather into large, crop-destroying groups
  • serotonin: a chemical inside the body that can change mood and behavior
  • gregarious: liking to live and move together in a large group
2

Questions

11 questions — every TOEFL Reading question type, in test order.

Q1 · Vocabulary
The word trigger in paragraph 2 is closest in meaning to
  1. A. the cause that starts something
  2. B. the result that follows something
  3. C. a warning sign of danger
  4. D. a small physical object
Answer
Correct: A
Q2 · Reference
The word That in paragraph 2 ("That sharp rise flips a switch inside the insect's body") refers to
  1. A. the touching between the grasshoppers' legs
  2. B. the sharp rise in the level of serotonin
  3. C. the switch inside the insect's body
  4. D. the phase change itself
Answer
Correct: B
Q3 · Essential Term
Based on the information in the passage, the term phase change can best be explained as
  1. A. the sudden rise in the level of serotonin inside the insect
  2. B. the process of forming a large flying swarm that can travel far
  3. C. any change in an insect's body size as it grows older
  4. D. a shift from a shy, solitary way of living to a bold, group-based way of living, triggered by repeated touching
Answer
Correct: D
Q4 · Factual Information
According to paragraph 2, what happens to the level of serotonin inside a grasshopper's body when its legs are touched again and again?
  1. A. It drops slowly over several days
  2. B. It stays exactly the same
  3. C. It rises sharply within a few hours
  4. D. It rises only after several weeks
Answer
Correct: C
Q5 · Negative Fact
According to paragraph 1, all of the following are true about locust swarms EXCEPT
  1. A. Adult locusts always live and travel completely alone
  2. B. A swarm can hold more than forty million insects in one square kilometer
  3. C. A swarm that size can eat as much food in a day as thirty-five thousand people
  4. D. Nearly every locust begins life as an ordinary, solitary grasshopper
Answer
Correct: A
Q6 · Sentence Simplification
Which of the sentences below best expresses the essential information in the highlighted sentence in paragraph 2? Incorrect choices change the meaning in important ways or leave out essential information.

Highlighted: "Because this touching happens again and again, the level of a chemical called serotonin rises sharply within a few hours."
  1. A. The rise in serotonin causes the grasshoppers' legs to keep touching each other.
  2. B. The chemical level inside the insect's body changes over time.
  3. C. Only when insects touch each other more than a hundred times does the serotonin level rise.
  4. D. Because the touching keeps happening over and over, the insect's serotonin level rises quickly, within just a few hours.
Answer
Correct: D
Q7 · Inference
Based on the information in paragraph 2, what can be inferred about a grasshopper that lives its entire life completely alone, with no crowding?
  1. A. It would develop a darker color and longer wings without ever being touched
  2. B. It would likely stay in the shy, solitary phase, since its legs are never touched repeatedly
  3. C. It would eventually form a swarm on its own, because all grasshoppers eventually become locusts
  4. D. Its serotonin level would rise gradually over many years even without touching
Answer
Correct: B
Q8 · Rhetorical Purpose
The author mentions the 2020 outbreak in East Africa in order to
  1. A. warn readers not to travel to East Africa
  2. B. explain in more detail how serotonin works inside the insect's body
  3. C. give a real, large-scale example of how the phase-change process described earlier can play out
  4. D. compare desert locusts with other kinds of grasshoppers found in Africa
Answer
Correct: C
Q9 · Paragraph Relation
How does paragraph 4 relate to the explanation of phase change given earlier in the passage?
  1. A. It presents a real event in which the mechanism described earlier actually happened on a large scale
  2. B. It argues that the explanation given earlier is incorrect
  3. C. It repeats the description of serotonin's role in more detail
  4. D. It explains the relationship between two completely different paragraphs earlier in the passage
Answer
Correct: A
Q10 · Insert Text
Look at the four squares [■] in paragraph 3 that indicate where the following sentence could be added.

This constant closeness keeps the chemical signal strong, so almost no insect switches back to the solitary phase.

Where would the sentence best fit?
  1. A. Square A
  2. B. Square B
  3. C. Square C
  4. D. Square D
Answer
Correct: B
Q11 · Prose Summary Select THREE · 2 pts
Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

Ordinary, solitary grasshoppers can transform into a destructive, swarming locust through a process triggered by repeated physical contact.

  1. A. A locust swarm covering one square kilometer can eat as much food in a day as thirty-five thousand people.
  2. B. Repeated touching between grasshoppers' legs causes a sharp rise in serotonin, which triggers a shift called a phase change.
  3. C. In the gregarious phase, the insects gather into growing marching bands and eventually form flying swarms.
  4. D. In 2020, this process caused a severe locust outbreak in East Africa that threatened food for millions of people.
  5. E. Locust swarms always travel over a hundred kilometers a day, no matter the weather conditions.
  6. F. Scientists first discovered serotonin's role in locust behavior through laboratory experiments in the 1990s.
Answer
Correct: B, C, D