Expert explains why there are so many dragonflies - The Times

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EDITOR'S NOTE: Rudolf Schilder, assistant professor of entomology at Penn State University, took some time to explain why Pennsylvania residents are seeing so many dragonflies this month. He studies dragonfly factors that impact their flight performance, usually in a laboratory.

QUESTION: Swarms of dragonflies have been so large that they have been picked up on radar. Is this common?

SCHILDER: Yes, these are likely (pre)migratory swarms or possibly feeding swarms. ... This species was observed in swarms around where we live (State College). Feeding swarms arise when there are sudden "outbreaks," or large assemblies of prey insects in a specific location.

Q: What are dragonfly migration patterns? Where do they go, and where do they come from?

A: That depends on what species of dragonfly we are talking about. Most dragonfly species will mate and produce eggs or larvae in the summer, which then will overwinter until the next spring. Those larvae will then become the summer generation of adults, which will repeat the process.

Some species, however, produce a migrating generation of adults during summer, which when the appropriate time arises, flies southward, after which a subsequent adult generation (produced in the South) will fly back north during spring. It is these species that you will likely find first around ponds in the northern U.S. during spring or early summer. The best-known example of such a species is the green darner. There is another famous migrating species of dragonfly, the wandering glider, which has a global distribution.

Q: Do they stay in hives or colonies, or are they independent?

A: Dragonflies are not social insects like, for example, honeybees. They will interact with one another quite directly, though, males in particular, during territorial disputes around ponds and springs. Having said that, the swarms we all heard so much about this year (although they happen every year) could be considered some alternate form of social behavior, I suppose, although to me it is more similar to shark behavior.

Q: What is their role in the ecosystem?

A: Dragonflies are predators of other animals, both larvae and adults. Larvae feed on larval insects (including mosquito and fly larvae) and can handle some vertebrates (e.g., tadpoles, small fish). Adults stick to insects; I have seen them eat many different (small and large) insects, but most of them will eat things like small flies, gnats, mosquitoes. Dragonfly larvae are prey to fish and amphibians, possibly other insect predatory larvae. The adults are hunted by birds, frogs and will get caught in spiderwebs.

Q: Are there any worries about their population?

A: While not as prominently featured in terms of decline as pollinator insects (e.g., bees, butterflies), dragonflies generally are considered at risk and declining, mainly due to the ongoing loss of the aquatic habitat (freshwater) they depend on throughout their lifecycle.

Rick Kazmer is a reporter for the Daily American in Somerset County, a GateHouse Media publication.

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