Dragonflies, along with other insects and birds, make a splash on Doppler radar


Swarms of dragonflies were first reported in northeastern Ohio, including Lorain, Cuyahoga, Erie, Mahoning, Columbiana and Trumbull counties earlier in the week. Sightings of dragonflies circling overhead extended south to Morrow, Knox and Licking counties midweek.

Video credit: Jennifer and Dennis Strohmeyer

The migrating insects were visible on National Weather Service Doppler radar: “While we are not biological experts, we have determined (through input from our followers) that it’s most likely dragonflies mixed with other insects/birds,” the NWS Cleveland said on Facebook.

Dragonflies normally migrate south from Canada and swampy areas surrounding the Great Lakes in mid-September, triggered by a cool spell, which commences the annual journey back to Florida and Mexico, where they overwinter.

Video credit: Kimberly Skeie

Green darners are one of 14 migratory species seen in the Ohio Valley region. The wandering glider is another Ohio visitor.

Dr. David Shetlar, Professor Emeritus of Urban Landscape Entomology at Ohio State, commented on the unusually dense swarms observed this year: “We had a super wet spring and early summer that created a lot of temporary water pools.”

In central Ohio, dragonflies tend to hover around bodies of water this time of year in search of insects to feed on, building up fat stores for the long haul of nearly a thousand miles or more. Ants release scents in the late afternoon, said Shetlar, so you are more likely to see these darting aerial acrobats in the evening.

He noted that dragonflies are harmless and do not possess a stinger, though a large one could potentially deliver a bite, if you put your finger in the jaw, amounting merely to a mild pinch.

The favorable weather conditions that left large swaths of standing water in the late spring provided fertile ground for female dragonflies to lay their eggs. An abnormally large hatch of nymphs several weeks later assured a dramatic crop of these beautiful insects.

Green darner is one of the common migratory species in Ohio. (Photo: Dr. David Shetlar, Ohio State University Entomology)

Robert LaPlante, Science Operations Officer at the NWS office in Cleveland, said: “We had nearly clear skies with a few cirrus… The radar indicates that the returns were non-meteorological, but classified as biological.”

The weak (light and fuzzy) returns were less than 20 dBZ (decibels), which if weather-related would have indicated mist or fine drizzle. LaPlante confirmed that there were “numerous reports of dragonflies swarming” that were likely migrating, though there was likely a “contribution to the radar reflectivity by other insects and birds.”

A beam of microwave radiation sent out by Doppler radar travels at a small tilt (0.5 to 19.5 degrees). The lowest elevation angle is apt to pick up precipitation targets, along with birds, bats and bugs. Energy is reflected by the objects and the returns are measured at the NWS radar site.

The intensity and speed of the pulse of the radar return or pulse determines how intense the precipitation is. An algorithm provides the color-coding to distinguish light rain from storms, along with other severe weather parameters in different radar modes.

Video credit: Cathy Kalo, Westerville

Shetlar noted that there was a dragonfly that slightly predates the dinosaur era possessing a three-foot wingspan, and among the earliest known flying insects.

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