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Surrounded by Swarms

What math can tell us about crowd behavior

FAO

A swarm of locusts takes to the skies above Madagascar.

Jim McMahon/Mapman™

Madagascar is a normally sunny island off the east coast of Africa. Yet for the past three years, the skies above it have occasionally turned black—with locusts! Swarms of the hungry insects are eating their way through the country’s crops.

Humans have dealt with locust swarms since the beginning of recorded history. The insects’ presence can mean disaster for a community. Anywhere from 40 million to 80 million locusts gather in an area about the size of 10 city blocks. Each insect tries to eat its own weight in food every day! A swarm can lead to food shortages and famine. 

What makes locusts act this way? When too many locusts appear in one place, they panic, says scientist Andrew Hartnett. He studies swarms at Princeton University in New Jersey. The insects go on a feeding frenzy, devouring anything edible. This includes farm crops and even other locusts.

Madagascar has been battling locusts since 2013. The insects are threatening the food supply for the country’s roughly 24 million people.Using airplanes loaded with pesticides, workers spray the infested areas to keep the locust population under control.

Swarms aren’t always trouble though, Hartnett says. Many kinds of animals swarm, from crabs to ants to bats. Swarm is just the word scientists use to describe how animals behave when they’re in large groups. Even humans can swarm. For example, you can see swarming behavior in a large crowd moving together on a street corner in New York City’s Times Square.

Swarms can even be a good thing. Without realizing it, we can “copy the behaviors of those around us,” says Hartnett. “Understanding collective behavior can teach us about our culture,” he says.

On Australia’s Christmas Island, a swarm of more than 100,000,000 red crabs migrates from the rainforest to the ocean each year. Each female crab lays 100,000 eggs. Fill in the blank to make the following statement true: 100,000,000 is ___ times as many as 100,000. 

The largest-recorded locust swarm in history was in the United States in 1875. The insects swarmed from North Dakota to Texas in an area about 100 miles wide and 2,000 miles long! Finish these number sentences:

____ x 100 ones = 10 x 10 tens = 1 hundred

2 × 10 hundreds = ___ hundreds = 2 thousands 

Scientists at Princeton University study the swarming behavior of golden shiners, a type of minnow found all over North America.

A. One large experiment tank can hold about 1,200 fish. On a separate sheet of paper, show how many hundreds are in that number using x’s.

B. Another tank can hold 10 times that amount. Write a number sentence in that calculates the total number of golden shiners in this tank. 

Red imported fire ants are native to South America, but they have invaded the U.S. Their colonies can be very large. Fill in the chart below to figure out the size of their colonies.

A swarm of locusts can contain 40,000,000 insects. A swarm that size can eat the same amount of food as roughly 40,000 people.

A. Fill in the chart with values representing the number of locusts and the number of people.Red imported fire ants are native to South America, but they have invaded the U.S. Their colonies can be very large. Fill in the chart below to figure out the size of their colonies.

B. How many times greater is the number of locusts than the number of people in the chart? 

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