The science of locust swarms

This exercise is a part of Educator Guide: Chemical Coaxes Locusts to Swarm / View Guide

Directions for teachers: After your students read the online Science News article “A single molecule may entice normally solitary locusts to form massive swarms,” ask them to answer the following questions. A version of the story, “Chemical coaxes locusts to swarm,” can be found in the September 12, 2020 issue of Science News. Students reading the print version should skip question No. 8.    

1. What are locusts? Why does the author describe them as both harmless loners and plagues?

Locusts are insects that live a mostly solitary existence and are generally averse to socializing, which is why the author describes them as harmless loners. But locusts also can gather in large swarms. When they do, the insects can destroy crops. This is why the author also describes locusts as plagues.

2. How large can locust swarms get?

Swarms can be composed of potentially hundreds of millions of locusts.

3. What area of the world is currently plagued by locusts? Why do you think the author included this information in the article?

East Africa is currently experiencing its worst locust plague in decades. The author included this information because it is a current event that relates to the science and offers an example of real-world implications.

4. What do scientists suspect causes locusts to swarm? How might it work?

Scientists think aggregation pheromones cause solitary locusts to form large groups. Locusts may release these chemicals into the air to signal other locusts to join them.

5. Name the molecule that scientists identified as a potential locust aggregation pheromone. What effect does it have on locusts?

The molecule scientists pinpointed is called 4-vinylanisole, or 4VA. Researchers say 4VA could function to coax solitary locusts to a swarm and keep swarms together.

6. What evidence do the scientists present supporting the claim that the molecule is an aggregation pheromone?

In lab tests, the molecule attracted locusts of all sexes and ages, as well as solitary locusts and locusts already in swarms. Concentrations of the molecule also grew as swarms grew larger. In field tests, traps laced with 4VA attracted more locusts than control traps.

7. List three ways this discovery could be used to improve locust control measures.

Traps laced with 4VA could congregate locusts in one place and thus allow more selective spraying of insecticides, protecting livestock and the environment. Scientists could develop a compound that blocks locusts from sensing 4VA. Scientists could also genetically engineer locusts so that they cannot sense 4VA.    
8. According to the online Science News article, what are potential drawbacks of some of the proposed measures?

Targeting 4VA might not stop swarms — factors including changes in behavior, metabolism and body size also are involved in swarm formation. The proposed measure to alter locusts’ genetic makeup could have off-target effects. Such effects would need to be well understood before genetically engineered locusts could be released into the wild.

9. What does the expression “smoking gun” mean? It is an example of a literary device called an idiom. Based on the context of the article, explain what an idiom is.

A smoking gun is conclusive evidence or proof of something. Idioms are expressions or phrases that are used to describe something unrelated to the literal meaning of the words in the expression or phrase.

10. Is there evidence that the newly identified molecule is the smoking gun when it comes to locust swarm formation?

While 4VA might be a smoking gun, meaning it has a role in swarm formation, it may not be the only compound or the most important — there may be other factors involved.