It is spring in the Northern Hemisphere, and one of the joys of spring is seeing the amazing migrations of birds as they move north from their wintering grounds. We watch the birds without thinking of the logistics that are involved in millions of birds moving over fast distances. How do you feed these hordes of living things? Their needs are even greater than usual because of the energy required for the long flights. We may not realize the importance of insect migrations that occur at the same time. What collateral benefits does this system create?
Dara Satterfield of the Smithsonian Institution in Washington, D.C. says, “Trillions of insects around the world migrate every year, and we’re just beginning to understand their connections to ecosystems and human life.” This migration not only feeds birds, but they pollinate wild plants and gobble agricultural pests.
We have written in our quarterly journal about the spring migration of monarch butterflies from Mexico to North America. In Europe and Africa, the migration is even more amazing and complex. Each spring the painted lady butterfly travels from Africa across the Sahara desert and the Mediterranean Sea into Europe and then retraces that journey in the fall. Because their life expectancy is so short, it takes six generations of butterflies to accomplish this migration. The butterflies avoid the extreme heat of North Africa in the summer, but they arrive in Africa just in time to feed from the flowers in the fall. Those butterflies are vital to the balance of living things in Europe.
Some of the insect migrations are very important to human food production. The marmalade hoverfly eats aphids during the larvae stage, and as adults they pollinate plants. The volume of insects is seen most clearly in the Pyrenees and Alps. Millions of hoverflies use the winds blowing through the mountain passes to get from one place to another. Scientists have been monitoring this migration because of its economic importance to agriculture in Africa and Europe. There is also a hoverfly migration in the western United States, but it has not been studied.
The size of these insect migrations is hard to comprehend, and we fail to understand the complexity of this system. Studies in the southern United Kingdom estimate that 3.5 trillion insects migrate over that area every year. Without those insect migrations, ecosystems on this planet could not exist.
The survival of living things in extreme conditions is always fascinating. There are places on Earth, such as the Sahara Desert, where the temperature on the ground can soar to 120 degrees Fahrenheit. Even in that extreme heat there are living things functioning very well in conditions that would be lethal to most forms of life.
Extreme survival is a way of life for the Saharan silver ants (Cataglyphis bombycina). The predators of these ants are desert lizards that retreat into their burrows in the heat of the day. Some of the ants keep watch to let the others know when the lizards are gone. Then the ant colony makes its food-search expedition. They come out into the full Sun and intense heat to scavenge animal carcasses. The picture shows them devouring an engorged camel tick.
The question is, “How do they survive the heat?” They have longer legs than most ants, and that keeps their bodies farther from the hot sand. They also travel across the sand at high speed (2.3 feet or 0.7 meters per second) using only four of their six legs to keep fewer feet on the ground. Also, their bodies produce heat-shock proteins that help their cells cope with the stress of the high temperature. Many animals produce heat-shock proteins, but not until they are exposed to extreme heat. The Saharan silver ants are programmed to produce those proteins before heat exposure to prepare them for what’s ahead.
Even with those adaptations, they are still exposed to the direct rays of the Sun. Scientists used electron microscopes to find the secret of the Saharan silver ant’s survival. The ants are covered with microscopic hairs that are not round or oval in cross-section like most hairs. They have a triangle shape to act as prisms. This shape reflects both the visible and infrared (heat) energy from the Sun away from their bodies. Because of these tiny prisms, the ants display a metallic shine. They look like metallic beads rolling quickly over the desert sand. No other desert creature has this form of reflection. Saharan silver ants are among the most heat-resistant creatures in the world.
One of the most interesting examples of design in living things is the ability that various forms of life have to migrate great distances for a wide variety of reasons. Sea turtles have an uncanny ability to return to the same beaches over and over to lay their eggs. Whales can travel long distances when they are ready to calve, giving their offspring a greater chance of survival. Migrations can be critical to animals or plants other than the animal making the migration. Sometimes the migration is critical to an environmental ecosystem. The salmon migration in Alaska, for example, is critical to the entire area sustaining plant life and a wide variety of animal life.
When insect migrations are studied, the question of how they make the migrations and why becomes even more complicated. Monarch butterflies make migrations of great lengths even though their life expectancy is too short for any single butterfly to make the entire migration. The champion of insect migrations is the globe skimmer dragonfly (Pantala flavescens). This insect has wide wings that look very delicate, but those wings can carry it for thousands of miles seeking wet seasons when it can reproduce. Migration has spread this insect’s DNA worldwide to every continent except Antarctica. Globe skimmers can fly for hours without landing and have been seen as high as 20,000 feet (6,200 m) in the Himalayas. They are sometimes called wandering gliders because they can glide on thermals in a way similar to birds. They seem to prefer moist winds, and they don’t stop for bad weather.