100 Species Confirmed in First Global Count
At least 100 species of dragonflies and damselflies migrate across continents, according to a global review published June 12 in Biological Reviews. Led by Dr. Johanna Hedlund of Lund University and the University of Exeter, the research confirms that some species, like the globe skimmer, complete multigenerational circuits between India and Africa by riding seasonal trade winds.
How do globe skimmers cross the Indian Ocean?
The globe skimmer (Pantala flavescens) completes a 2,500-kilometer flight from northeastern India to the Maldives in a single crossing. These insects weigh roughly 300 milligrams—less than a standard paperclip—yet they survive the journey by exploiting the Inter-Tropical Convergence Zone (ITCZ).
According to a 2021 energetic flight model published in Frontiers in Ecology and Evolution, these dragonflies can’t rely on fat stores alone. Continuous flapping would exhaust them in four hours. Instead, they alternate between active flapping and passive gliding on rising air, which keeps them airborne for 230 to 286 hours.
Timing is everything. The insects launch during the seasonal passage of the ITCZ, where trade winds provide high-altitude tailwinds. The 2021 model found that only 15% of autumn trajectories from India to Africa succeed. Spring crossings are more reliable, with a success rate of roughly 40% due to more favorable wind geometry.
Why is dragonfly migration a signal for climate change?
Dragonflies act as biological indicators for shifting planetary systems. Because they depend on precise wind patterns, any change in ocean surface temperatures that shifts the ITCZ could collapse their migration corridors. If the 15% success rate for autumn crossings drops further, the entire population circuit faces extinction.
Dr. Hedlund notes that some species are already shifting their ranges. The vagrant emperor (Anax ephippiger), originally a North African species, is now a regular breeder in the United Kingdom and Scandinavia. This northward expansion tracks the movement of thermal conditions required for the species to survive.
The ripple effect on global food webs
A collapse in dragonfly migration wouldn’t just affect the insects. Millions of dragonflies provide a massive pulse of biomass and nutrients to wetlands on two continents. Predators that time their lives to these arrivals would lose a primary food source.
What is the link between dragonflies and Amur falcons?
The globe skimmer doesn’t travel alone. Amur falcons, small raptors that winter in southern Africa, follow an ocean crossing route that mirrors the dragonfly’s path with precision. According to data cited in the Biological Reviews study and Wikipedia, the falcons prey on globe skimmers during the most difficult segments of the crossing.
GPS tracking of Amur falcons corresponds closely with the wind trajectory simulations generated for the dragonflies. This suggests both species use the same “atmospheric highway,” with the falcons exploiting the insects as an in-flight fuel source over open water.
How does wing chemistry track insect movement?
Since dragonflies are too small for traditional GPS tags, scientists use stable isotope analysis. When a dragonfly is a nymph in freshwater, it absorbs hydrogen from the local water. This hydrogen becomes locked into the wing’s chitin as the insect matures.
Because hydrogen isotope ratios vary by latitude and rainfall, the wing acts as a geographic fingerprint. A 2012 isotope study used this method to prove that dragonflies intercepted in the Maldives had originated in northern India, having already flown over 2,000 kilometers.
Comparison: Traditional Tracking vs. Isotope Analysis
| Method | Applicability | Limitation |
|---|---|---|
| GPS/Radio Tags | Large birds, mammals | Too heavy for small insects |
| Isotope Analysis | Insects (wing chitin) | Shows origin, not real-time path |
Frequently Asked Questions
How far do globe skimmers migrate?
Individual globe skimmers fly over 2,500 kilometers from India to the Maldives. The total multigenerational circuit between India, the Maldives, and East Africa covers an estimated 14,000 to 16,000 kilometers.
Do dragonflies use a map to navigate the ocean?
No. They are essentially passengers on an atmospheric conveyor belt. They ascend to altitudes above 1,000 meters and orient themselves into the tailwinds produced by the Inter-Tropical Convergence Zone.
Why are only 1.5% of dragonfly species migratory?
The review led by Dr. Johanna Hedlund found that while migration has evolved independently multiple times across four dragonfly and two damselfly families, it remains a specialized strategy used by a small minority of species.
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