Area residents have seen swarms of dragonflies in the county recently, but those swarms are not entirely uncommon, though seeing them may be.
“To the best of my understanding, (dragonfly swarms) are not an uncommon event, but it is one of those things that’s rarely seen,” said Joy Hosler, professor of biology at Juniata College. “There are swarms that are happening, but we’re usually not noticing them for whatever reason.”
Hosler said dragonfly swarms, which have been prevalent enough to be picked up on weather radar, are commonly associated with two events.
“There are feeding swarms, and dragonflies are collecting in one area because there’s a rich food source,” he said. “It’s likely a Mayfly hatch, or there’s food around.
“The ones we’re seeing right now, however, they’re migration swarms,” Hosler added. “It’s not entirely clear on what triggers a migration swarm, as the research is not extensive.”
Research indicates that dragonfly swarms likely occur after a cold front has passed through the area, said Hosler.
“Researchers think the cold front passing through is a cue to dragonflies it’s time to head south for the winter,” he said. “They’re going to end up migrating like birds and monarch butterflies do.”
Though they may be heading south, where they end up is unknown.
“It’s not entirely clear where they are headed,” said Hosler. “There have been swarms identified over the Gulf of Mexico, and those swarms show up in Mexico, so the thought is they may be migrating over Central America.
“The thing is, dragonflies don’t live very long — no longer than a season,” he added. “Those that are migrating south, scientists think they’re migrating to warmer climate, having babies. Then, their babies will hatch, then fly north in the summer time to feed.”
While it’s been dry in recent weeks, a wet, warm start to the summer may be mean a bumper crop for dragonflies in the area, so when they do swarm, people will notice more.
“Dragonflies spend most of their time around water, where they lay their eggs,” said Hosler. “They’re in less populated areas around water.”
People on Facebook have said they’ve noticed dragonflies in areas from Shirleysburg to Hesston and Alexandria.