Have you seen large numbers of dragonflies in recent weeks? I’ve had contacts from Missourians in several locales reporting the noticeable massing of dragonflies.
There are a couple of reasons dragonflies will congregate. They are predatory on small, flying insects and will gather in large numbers for feeding where their food supply is plentiful. This often takes the insects to feeding locations away from streams or ponds, and people are sometimes surprised to see them away from water. While tied to water for egg-laying and nymph development, flying adults will visit many habitats far removed from water. Some species of dragonflies migrate in late summer and fall and will gather into larger swarms for long-distance migration. It is hard to make general statements about dragonflies because Missouri has more than 80 species and their behavior varies. Some species don’t migrate, while others do. One species, the green darner, has a resident population as well as a migratory one.
Studies of dragonfly migration, using tiny radio transmitters on the insects, have indicated similarities to bird migrations. They tend to migrate in response to cooler, nighttime temperatures and will take advantage of northwest winds associated with cold fronts. Movement is not continuous, with flight days interrupted by days of rest and feeding. The destination of the southward-moving insects ranges from peninsular Florida to Central America. American kestrels’ migration is often concurrent with dragonfly migration and the small falcons will feed on the insects as both groups move south. Fall-migrating dragonflies only make a one-way trip. Those that come north in spring are adult insects of the next generation, originating from eggs laid in southern waters.
I find that dragonflies are like many other biological groups of which I have limited knowledge. With a little investigation, I find that there’s much more diversity and fascinating behavior in the group than I might have expected. Surprising interactions with other species reinforce the picture of the ecosystem as a functioning whole composed of many interconnected parts.