Feb 202 min read

Birds aren't the Only Ones

Spring means migration time for birds and birders. But birds aren’t the only animal with wings that migrate. Monarch butterflies are famous for traveling long distances each year, but they’re not the only insects that migrate. Many butterflies, moths, and dragonflies take to the air for seasonal migrations, and although they’re quiet about, it some travel hundreds or thousands of miles. The success of their journey largely depends on the habitat they encounter along the way.

Tiny brown planthoppers on stem of plant — Brown Planthopper

People were once skeptical that insects could migrate long distances. Historically, scientists assumed an organism so small and short-lived couldn’t move more than a few miles. As we now know, they can. Bogong moths (Agrotis infusa) in Australia can migrate over 1000 km (621 miles) every spring. Danaid butterflies (cousins of monarchs) in Taiwan migrate over 300 km (186 miles) in the fall. Wandering glider dragonflies (Pantala flavescens) cross the Indian Ocean. The brown planthopper (Nilaparvata lugens), a tiny insect only 4 millimeters (.16”) long, migrates over 200 km (124 miles) in China. These are just a few of the hundreds of insect species around the world that make incredible journeys.

By the mid-1900’s scientists finally recognized insects could move long distances; but still, they assumed insects were being haphazardly blown by the winds, unable to control their direction. In recent years migrating insects like the Silver Y moth (Autographa gamma) provided evidence to contradict that theory, showing, instead, that insects selectively choose directional winds to maximize their speed, allowing some to fly up to 650 km (400 miles) a night.

Many insect populations have adapted to make round-trip migrations over the course of a year, with the help of multiple generations. Painted lady butterflies, for instance, fly north out of Mexico in the spring to travel to the northern U.S. and Canada; later, their grandchildren or great-grandchildren return south in the fall. Monarchs behave similarly. A handful of insect species engage in single-generation migrations, where the same individual moves during one season and returns a few months later.

In eastern North America there are over 30 insect species that migrate north in the spring and south in the fall. They include the Common buckeyes (Junonia coenia), American lady (Vanessa virginiensis), Cloudless sulphur (Phoebis sennae), Question mark (Polygonia interrogationis), Mourning cloak (Nymphalis antiopa), Red admiral (Vanessa atalanta), Common green darner (Anax junius), Wandering glider (Pantala flavescens) and the Milkweed Bug (Oncopeltus fasciatus).