Locust

Most grasshoppers like to live alone.

But sometimes, things change. If there is a dry time and then lots of rain, many grasshoppers grow close together. This makes them change. They start to act as a big group.

These groups are called swarms. They move together in huge clouds. They can fly very far. The swarms eat lots of green plants. This can hurt the food on farms.

People have seen these swarms for a long time. They are even shown in old art. Some people in many lands eat them as food. It is amazing how they change!

Most grasshoppers like to live alone. But some species can change. They become locusts when they live in large groups.

This change happens when many insects live close together. It often starts after a dry time and then heavy rain. This rain makes many green plants grow. When grasshoppers crowd together, they touch each other a lot. This touch causes a change in their brains. A chemical called serotonin is let out in their brains.

This chemical makes them change in many ways. They change color and eat much more. They also breed more easily. They form large groups called swarms.

Swarms move across the land like a single unit. They can be billions of insects. These groups can eat most of the green plants in a field. This can destroy crops on farms. People have known about locusts for a very long time. They are shown in old art from ancient Egypt. In some lands, people even eat them as a special food.

Locusts are a special kind of short-horned grasshopper. Most of the time, these insects live all by themselves. They are called solitary when they live this way. However, some species can change their whole way of life. They become gregarious, which means they like to live in groups. This change happens when they form huge swarms. Scientists do not use different names for locusts and grasshoppers. Instead, they use the word locust to describe a grasshopper that swarms.

This change is a way the insect adapts to its world. It often starts after a long drought. When rain finally comes, green plants grow very fast. This provides lots of food for the insects. As more insects arrive, they begin to crowd together. This crowding causes them to touch each other often. Touching the hind legs many times per minute triggers a change. A chemical in the brain called serotonin is released. This causes the insects to change color and eat much more. They also begin to breed much more easily.

People have studied these amazing changes for a long time. A scientist named Boris Uvarov helped explain how they work. He studied the migratory locust in the Caucasus region. He discovered that the solitary and swarming phases were actually the same kind of insect. He gave the two phases the names solitaria and gregaria. Other researchers like Charles Valentine Riley and Norman Criddle also helped us understand them. These studies helped people learn how to control the swarms.

Locust swarms can be truly enormous. A single large swarm might have billions of insects. They can cover thousands of square kilometers of land. In some places, there can be 80 million locusts in just one square kilometer. One famous plague happened between 1966 and 1969. It covered parts of Africa, the Middle East, and Asia. During that time, the number of locusts grew from two to 30 billion. In 2013, a plague in Madagascar covered half the country.

Locusts have been part of human history for thousands of years. Ancient Egyptians carved them on tombs between 2470 and 2220 BC. They are also mentioned in the Bible, the Quran, and the Iliad. Because they eat so many plants, they can cause famines. In some countries, people consider them a delicious food. They are even used in classrooms to study how animals work. Today, we use planes and new biological tools to watch and control them.

Locusts are specialized short-horned grasshoppers belonging to the family Acrididae. While most grasshoppers live solitary lives, certain species possess the ability to change their behavior and physical form. This transformation occurs when populations become dense enough to trigger a swarming phase. Scientists do not make a taxonomic distinction between locusts and grasshoppers. Instead, the term "locust" refers to any grasshopper species that undergoes this transition. This biological phenomenon is known as phase polyphenism, where one species can take on different forms.

The transition from a solitary life to a gregarious one is driven by environmental changes. Usually, a period of drought is followed by rapid vegetation growth. This creates ideal conditions for the insects to breed abundantly. As the population increases, the insects begin to crowd together. This crowding leads to increased tactile stimulation of their hind legs. When an insect experiences several contacts per minute over a four-hour period, its brain releases serotonin. This chemical change triggers a dramatic shift in the insect's biology. The locusts change color, eat significantly more, and begin to breed much more easily.

Locust populations progress through several distinct stages of growth. An "outbreak" occurs when the first bands of gregarious nymphs, also called hoppers, form. If these groups grow larger, the event is called an "upsurge." When many upsurges join together across a large region, it becomes a "plague." The physical differences between the phases are quite striking. In species like the desert locust, the gregarious nymphs become darker with yellow and black markings. They also grow larger and have a longer nymphal period. The adults develop different body proportions and higher metabolic rates. They mature more rapidly and reproduce earlier, though they have lower levels of fecundity.

History shows that locust plagues have impacted humans for millennia. Ancient Egyptians carved locusts onto tombs between 2470 and 2220 BC. The insects appear in many ancient texts, including the Iliad, the Bible, the Quran, and the Mahabharata. These swarms can devastate crops and cause widespread famine or human migration. In the ninth century BC, Chinese authorities even appointed specific officers to fight locusts. Some historical records suggest that locust plagues were linked to human disease outbreaks. For example, a pestilence in China in 311 AD was blamed on locusts. This may have been caused by rats eating the locust carcasses and spreading disease.

The scale of a locust plague can be difficult to imagine. A single large swarm can consist of billions of individual insects. These swarms can spread across thousands of square kilometers. In some extreme cases, populations can reach 80 million locusts per square kilometer. One massive plague in Africa, the Middle East, and Asia lasted from 1966 to 1969. During those two generations, the population grew from just two insects to 30 billion. More recently, a 2003 to 2005 infestation in West Africa cost $122 million to manage. The damage to crops during that period reached up to $2.5 billion.

Researchers have studied these insects to understand their complex life cycles. Boris Uvarov was a key figure who analyzed the different phases of the migratory locust. He discovered that the solitary and gregarious phases were not separate species. He named these phases "solitaria" and "gregaria." Other scientists, such as Charles Valentine Riley and Norman Criddle, also contributed to our understanding. Today, scientists use modern surveillance to track breeding grounds. Traditional control methods involve using insecticides from the ground or the air. Newer biological control methods are also proving to be effective at managing populations.

Locusts are found on almost every continent except Antarctica. The desert locust is perhaps the most famous due to its ability to migrate long distances. The migratory locust is also widespread, appearing in Africa, Asia, Australia, and New Zealand. In North America, the Rocky Mountain locust became extinct in 1902. However, the High Plains locust reached plague proportions during the Dust Bowl in the 1930s. Interestingly, locusts have a very long evolutionary history. A fossilized wing found in Iran suggests that locusts may have been migrating for at least 30 million years. This shows how deeply these insects are connected to the history of our planet.