Dragonflies are a common sight in many parts of the world. Across the globe, there are approximately 3,000 known species of dragonflies, inhabiting diverse environments. Their widespread presence often prompts a curious question: do these seemingly delicate creatures undertake long, arduous journeys across continents and oceans?
The Migratory Phenomenon
While not all dragonfly species engage in long-distance travel, a notable number do undertake significant migrations. Among the most recognized migratory species are the Common Green Darner (Anax junius) and the Wandering Glider (Pantala flavescens). Dragonflies migrate for several reasons, often influenced by environmental cues such as changing seasons, dwindling food supplies, and the necessity to find suitable breeding habitats or warmer climates.
The Common Green Darner, for instance, exhibits a multi-generational migratory pattern across North America. This species typically migrates northward in the spring and southward in the autumn, with different generations completing segments of the full journey. Their migratory movements are largely influenced by temperature, often beginning when temperatures reach around 9 degrees Celsius.
The Wandering Glider, also known as the Globe Skimmer, is renowned for its extensive, trans-oceanic migrations. This species is found on nearly every continent, making it the most widespread dragonfly globally.
The Incredible Journey
Dragonflies are skilled fliers, capable of hovering, cruising, and gliding. They effectively conserve energy by utilizing air currents.
Migratory species often possess specific wing adaptations, such as elongated forewings and larger hindwings, which enhance their endurance. Their specialized flight muscles also allow for independent wing control, enabling complex movements.
These insects can achieve high speeds and altitudes during migration. The Common Green Darner can fly up to 58 kilometers per hour and has been recorded covering 122 kilometers in a single day. The Wandering Glider is known to ascend to high altitudes, with sightings over 6,000 meters in the Himalayas. They often ride high-altitude seasonal winds to traverse vast distances.
The Wandering Glider’s migrations are among the longest known for any insect. Individual gliders can fly over 6,000 kilometers, contributing to annual multigenerational journeys that span up to 18,000 kilometers. This species is noted for crossing oceans, including a 3,500-kilometer flight over the open Indian Ocean. For the Common Green Darner, individual migrations can exceed 600 kilometers, with some individuals traveling more than 2,500 kilometers. These journeys present challenges, including the need to find adequate food sources and suitable breeding sites along their routes.
Unraveling Migration Secrets
Scientists use various methods to study and track migratory dragonflies. Visual observations provide initial insights into their movements, often supplemented by citizen science initiatives. Projects like the Migratory Dragonfly Partnership engage the public in monitoring dragonfly movements, contributing valuable data that helps researchers understand the environmental factors triggering migration.
Traditional tagging methods are challenging for these small, fast-flying insects, but miniaturized radio transmitters weighing around 300 milligrams have been used successfully on species like the Common Green Darner.
Another significant tool is radar tracking, where specialized entomological radars can detect and classify flying insects by their size, shape, and alignment. Even weather radars, such as NEXRAD, can be repurposed to track insect concentrations, providing data on their height, speed, and direction.
Stable isotope analysis offers a method to determine the geographical origins and migratory paths of dragonflies. This technique involves analyzing the ratios of hydrogen isotopes present in a dragonfly’s wings. Dragonflies incorporate specific isotopic signatures from the water in which they develop as nymphs, and these signatures remain locked in their wings throughout their lives, revealing their birthplace and tracing their long-distance travels.