monarch butterflies
September 25, 2014

Were Monarch Butterflies Responsible For Unusual Weather Radar Readings?

Chuck Bednar for redOrbit.com - Your Universe Online

Large blue blobs appearing on weather radar last week above southern Illinois and central Missouri likely belonged to a swarm of Monarch butterflies, according to officials at the US National Weather Service in St. Louis.

According to Kim Bell of the St. Louis Post Dispatch, the radar masses indicated the presence of moderately heavy rain, but those readings were observed on a day that was otherwise bright and clear. There was no trace of bad weather to explain what meteorologists were seeing.

“Keen observers of our radar data probably noticed some fairly high returns moving south over southern Illinois and central Missouri,” the NWS posted on its Facebook page last week. “We think these targets are Monarch butterflies.”

Image above credit US National Weather Service Saint Louis Missouri.

The agency concluded that the blobs were most likely biological in nature due to the “high differential reflectivity values” and the “low correlation coefficient values.” High differential reflectivity indicates these are flat or oblate targets, while the low correlation coefficient indicates that the targets were changing shape.

Both of those traits are explainable by Monarchs, which would appear to be oblate while in flight and would seem to be changing shape as they were flapping their wings. According to Doyle Rice of USA Today, the butterflies were most likely migrating southward en route to spend the winter in Mexico.

Becky Oskin of LiveScience said that forecasters believe the swarm of butterflies was flying between 5,000 feet and 6,000 feet (1,525 meters to 1,825 meters) above the ground. Likewise, the timing indicates that the blob’s movements matches up with a recent exodus of Monarchs from the Great Lakes region.

“The monarchs may have gathered together because of favorable weather conditions. Monarchs take advantage of air currents to soar like birds, conserving energy for their two-month trip to Mexico. Sometimes the butterflies fly in ones or twos, but swarms of dozens or hundreds of stunning orange-winged insects have been sighted by people tracking their migration,” she added, citing information obtained from the nonprofit group Monarch Watch.

The butterflies have been under duress this spring due to an ongoing drought, as well as an unexpectedly cold winter and a lack of their primary food source (milkweed), said Rice. Furthermore, this incident does not mark the first time that weather radar has detected biological matter this year, having already spotted grasshoppers in New Mexico around Memorial Day and mayflies in Wisconsin in July.

Not everyone is convinced that the radar masses were really butterflies, however.

“If there are enough monarchs migrating through to cover a 200-mile stretch of land at one time, that would be a great thing,” Wendy Caldwell, program coordinator for the Monarch Joint Venture at the University of Minnesota, told Bell. “But without more evidence, I would be hesitant to believe it. It could certainly be living things. There are many birds that migrate and dragonflies. It isn’t necessarily monarchs.”