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Insect Investigation: Cicadas and Locusts Not the Same

You might be familiar with cicadas because of the loud buzzing sound they create each summer. Some people refer to these bugs as locusts, but cicada and locusts are not one and the same. They aren't even closely related.

A cicada on a leaf with its molted exoskeleton behind it.
A cicada. (Photo by Glenn P. Knoblock)

Of cicadas and locusts, only one — the cicada — lives in the United States. This hasn't always been the case, however. At one time, the Rocky Mountain locust could be found across parts of America, but it was declared extinct in the early 1900s.

Both cicadas and locusts can be viewed negatively, but for very different reasons. Cicadas are actually beneficial insects that only impact our enjoyment of the outdoors because they are noisy. Locusts can and have had highly destructive effects on crops for centuries, dating back as far as ancient Egypt.


Words to know

Aerate: To introduce air into.

Devour: To each quickly.

Famine: Extreme scarcity of food.

Gregarious: Sociable or fond of company.

Nymph: Immature form of an insect.

Solitary: Done or existing alone.

Swarm: A large, dense group in insects.


Locusts are a kind of grasshopper, and they look like other grasshoppers we see. Unlike other grasshoppers, locusts sometimes form enormous swarms that can devour plants, often entire fields of crops. The locusts are normally solitary, so when swarms develop it can have a devastating impact on the agricultural industry. Only 22 of the thousands of grasshopper species that exist in the world are locusts.

Swarms of locusts result from a specific weather pattern. When prolonged dry weather occurs, the locusts must gather in areas where they can find vegetation to eat. This causes the insects to release a chemical called serotonin, which affects their behavior and appetite. Then, when rain breaks the dry spell and green vegetation is easier to find, the locusts switch from their normal solitary lifestyle to what is called a gregarious phase.

During the gregarious phase, the locusts reproduce more rapidly and become even more crowded into spaces. They will also sometimes change their color and even their body shape, and their brains get bigger.

Swarms can include millions of locusts, and they can consume more than 300 million pounds of vegetation in a single day! They travel as they consume the vegetation, and they can sometimes travel great distances. In 1988, a swarm of locusts traveled 3,100 miles from West Africa to the Caribbean in 10 days.

We don't experience locust swarms in the United States because we no longer have locusts in North America, but they do occur in many other parts of the world. They are most destructive in certain regions of Africa, where the loss of agricultural crops can cause starvation and famine.

We are fortunate not to experience the devastating effects of locusts in the United States, but we do experience the presence of cicadas. Here in Illinois, we have two different kinds of cicadas, dog-day cicadas, also called annual cicadas, and periodical cicadas.

Periodical cicadas are the ones that draw headlines when they emerge from underground every 17 years, or 13 years in southern Illinois and other parts of the United States. Dog-day cicadas also have multi-year life cycles, but they can vary from two to eight years depending on the species. Because their life cycles vary, we experience dog-day cicadas each summer to varying degrees, usually between July and September.

There are more than 3,000 species of cicadas in all. Both dog-day and periodical cicadas make the loud buzzing sound we associate with these insects. Much like crickets and other insects, the purpose of the sound is to attract a mate. Only the males produce the sound, which they do by vibrating membranes on their abdomens.

Prior to their emergence, cicadas spend nearly all their lives underground. Eggs are laid in tree limbs. When the nymphs hatch, they feed on fluids from the tree then fall to the ground and burrow into the earth. They will stay there for between two and 17 years, depending on the species. While underground, they feed on tree roots.

Large populations of cicadas can sometimes cause damage to young trees, but they are not considered destructive. They serve several beneficial purposes in the ecosystem. They are a food source for many other animals, and the cicada nymphs that live underground help aerate the soil.


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