Migratory Insects: Types & Causes

Instructor: Amanda Robb
In this lesson, we'll be learning about different types of insect migrations. We'll examine a few of the main reasons insects migrate and look at different examples of insects that migrate for each cause.

What is Migration?

Every year, millions of people go on a pilgrimage to a sacred site based on their religious beliefs. For example, people of the Hindu faith travel to the Ganges River in India for the festival of Kumbh Mela. Similarly, Muslims pour into the holy city of Mecca for the hajj, a pilgrimage that is required in the Muslim faith.

Although these spiritual journeys are part of many of our lives, most humans do not travel like this for a specific cause. Sure, we may jump on a plane to see our relatives across the country, but visits are short and not necessarily occurring at one time of year.

But, for many types of animals, this type of travel is part of their lives; a process called migration. Migration is the movement of populations of animals from one habitat to another. Usually, it is seasonal with a specific route, but some animals migrate based on environmental conditions and their travel is not predictable. In all cases, migration is an innate behavior triggered by specific changes in the environment.

Large animals, like zebra and wildebeest, migrate. But, some of the most well-known migrators are insects. These tiny creatures can travel surprisingly long distances during migration.

Causes

Insects migrate for a variety of reasons. First, many insects migrate to find food sources. When food runs low and crowding begins, insects move to better climates with more abundant food sources.

In the winter, you might notice the absence of many insects that plague us during the summer months. That is because insects often migrate as a consequence of changes in climate. Winter often brings hostile weather, which can be especially hard for insects since they cannot regulate their body temperature as we do.

Insects may also migrate to mate. They travel long distances to specific mating grounds to lay their eggs. Today, we're going to look at two examples of insects that migrate and explore the reasons they take on their cyclical journeys.

Desert Locust

The desert locus has been the star of Biblical plagues for hundreds of years. Unfortunately, plagues of locusts are a real thing and still happen today. Desert locusts are small insects related to grasshoppers, but they are not the pleasant jumping bugs you see in the meadow. Desert locusts form immense swarms that migrate long distances to live in more favorable conditions with more plentiful food sources. Swarms can be as large as 460 square miles in size, with 80 million locusts occupying a single half a square mile.

Hundreds of millions of locusts gather in a swarm for migration
locust swarm

Thankfully, locusts do not swarm in a predictable yearly fashion. So, what is the driving force behind this large-scale relocation? To understand this, we must look at the locust life cycle.

Scientists believe that locusts exist in a solitary stage and a gregarious stage. In the solitary stage, adult locusts blend in with their surroundings, live mostly alone, and have a low metabolic rate.

In the gregarious stage, locusts not only change their behavior, but they also change their appearance. Their green camouflage turns into bright orange and black stripes. They congregate in large groups, becoming more active.

Locusts are infamous devourers of plants. When there are heavy rains, the abundance of food drives causes the usually solitary locusts to gather together into the area.

However, if the rain is followed by a drought, the locusts find themselves crammed together without a reliable food source. The high density of locusts and hostile environment cause chemical changes which trigger a shift to the gregarious stage.

Morphological differences between the solitary and gregarious phases
locust phases

Since the environment they are in is no longer hospitable, these locusts take to the skies in enormous packs that cloud the air, covering any and all surfaces in their path. The locusts cover so much space that it can be incredibly difficult, if not impossible, to stop the swarm. With their voracious appetites, they devour both natural plants and crops. When there are favorable conditions again, such as rainfall and temperate surroundings, the locusts will revert to their solitary form and stop their migration.

Monarch Butterfly

Although swarms of locusts can be a horrifying plague, swarms of butterflies don't seem so bad. Monarch butterflies are easily identified by the striking orange and black pattern on their wings.

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