Wetter weather brings huge numbers of dragonflies
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Some Marshalltown residents were "bugged" when swarms of dragonflies migrated through town last week.
Marshall County Conservation Director Emily Herring said the insects are migrating south, and the more likely reason for the large number was air movement from a weather front, prompting the migration. However, she could not say with absolute certainty as to the reason for the significant increase.
"My guess is that it was wetter this year, which benefited their population," Herring said. "Not only does the extra wetness provide sources for them to reproduce, it also provides them with food as dragonflies consume the larva and adult mosquitoes."
Dragonflies are also bioindicators of high-quality water as their larvae need the high quality in order to survive, she added.
Seeing the dragonfly increase is normal this time of year for Marshall County.
"They often travel at the same time monarch butterflies do," Herring said. "More than likely they were green darner dragonflies that over winter south to Florida. Unlike monarchs, there are two different populations – one that overwinters as a nymph in frozen water and one that migrates."
The green darner migrates south to Mexico. Common food sources for it are flies and wasps.
Wednesday brought a "significant increase" in dragonfly numbers. Herring said residents will probably see a trickle amount come through until the next front.
"By the end of October, there will be very few," she said.
While the large influx of dragonflies is normal this time of year at Grimes Farm, where Herring's office is located, what was surprising was how many were within Marshalltown. In the yards of some houses, large numbers hovered, flew and dove not too far above the ground. In nearby yards, there might have been a few dragonflies or none at all. Herring said the yards more than likely provided a good place for food or shelter. Plus, dragonflies stay in groups to avoid predation.
"Their main predators are birds, so less trees mean less predators perching in trees," she said. "When you see dragonflies, they are usually in wide open areas."
Herring suggested that residents enjoy observing the dragonflies.
"They are pretty amazing to watch," she said. "They are beneficial predators of mosquitoes and other insects that we consider pests. They are also an important part of the food web, providing food for sources for birds, fish and amphibians."
Contact Lana Bradstream at 641-753-6611 ext. 210 or lbradstream@timesrepublican.com.