One of the most amazing things we see in the natural world is the ability of some living things to make incredible migrations. In the past, we have described the monarch butterfly’s migrations from wintering areas in Mexico to northern parts of the United States covering a round trip of about 10,000 kilometers. However, we see that painted lady butterflies out-migrate monarchs.
Scientists have studied how the monarchs navigate such incredible distances with formidable obstacles in their way. Biologists have proposed a variety of models as to how these fragile butterflies could acquire such an ability. However, in the case of the monarchs, the journey is not made by a single butterfly but by a succession of generations.
Science News for July 21, 2018 (page 4) told about a study of another butterfly with an amazing migration. It has the scientific name Vanessa cardui and is commonly known as the painted lady butterfly. These butterflies live in Southern Europe and migrate to Africa in the fall–a distance of 12,000 km. That’s 2000 kilometers farther than the monarchs, and the journey involves crossing the Sahara Desert. As with the monarchs, scientists had believed that the migration involved several generations. New techniques allowed researchers to put markers on the painted ladies when they were caterpillars. We now know that at least some of the butterflies make this incredible journey in one lifetime.
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.
It is easy for humans to minimize the design that is needed for life to exist on Earth. How do you feed massive numbers of birds, especially in the spring when winter has taken away most of their food sources, and their food needs are maximized as they lay eggs and feed baby birds? In the past scientists have shrugged their shoulders and imagined that there are food sources we don’t recognize that fill this gap until the summer season generates sufficient seeds and insects to sustain the growing populations. Similar problems exist for many other animals like bats that depend on insects for their nutritional needs.
In the April 2017 issue of Scientific American (page 84), there is an interesting report about previously unknown migrations of insects. We have known about monarch butterflies for some time, but this study by British researchers shows that migrations of insects are massive. Over southern Britain alone there are 3.3 trillion insects migrating. That is an average of 3200 tons of bugs moving through the skies over Britain every year. The study also reports that similar patterns have been observed in Texas, India, and China.
The complexity of this migration is astounding. Insects don’t live long enough for one bug to complete the migration. Researchers found that in some cases six generations were involved to complete a migration. The insects do not just get randomly blown about. They travel in a well-programmed pattern taking advantage of wind direction and speed. The elevation at which they fly to get the strongest support for their journey is carefully chosen. For a number of reasons, spring migrations are different from fall migrations.
Over the years we have presented data on some amazing migrations. We have had several discussions about the Arctic tern and how it makes its incredible 12,000-mile journey. Research has shown that the Arctic tern uses multiple cues including magnetism, sight, smell, and even sound. We have also talked about whales, salmon, and sea turtles and the way they benefit multiple ecosystems by their migrations. Now we have a new migration that has just been discovered and is equivalent to 20,000 flying reindeer. It’s migrating insects.
According to the study, 2-5 million migrating insects fly over the United Kingdom each year. The study is reported in the December 23, 2016, issue of Science by a team headed by Jason Chapman. Tracking these arthropods involves the use of special radar designed to detect insects. The team estimates that the total biomass of these arthropods is 3200 tons which is 7.7 times more than the biomass of the songbirds in the same area. These are tiny creatures with some of them weighing less than 10 milligrams.
Chapman notes that these arthropods are not just accidentally caught up in the wind. Some of them climb to the top of a plant to launch their flight. Some stand on tiptoe and put out silk until the wind catches them and carries them away. The animals only launch when the wind is to the north from May to June, and in August and September, they launch when the wind blows to the south. Chapman concludes “these arthropods must have some kind of built-in compass plus a preferred direction and the genetics that change that preference as they or their offspring make the return migration.“