A chiseled line shaded green, yellow and red appeared on weather radar in Oklahoma City on Saturday night, but it wasn’t rain. It was a cold front chock full of butterflies and other bugs.

The gathering of friendly insects occurred along a wind shift line that passed through the Oklahoma City metro area Saturday evening between 5:30 and 6:00 p.m.


That line on radar isn't rain. It's from butterflies (and dragonflies) caught in the wind shift. Winds from the north carried the insects south. (GR2 Analyst)

Butterflies, dragonflies and likely other bugs surfed the front by the thousands. Doppler radar from the National Weather Service in Norman indicates the butterflies likely were present to a height of about 2,500 feet. Many of the insects were swept up in the leading edge of the southward-moving air, with others trailing in its wake.

Monarch butterflies are known to migrate south for the winter, the peak of their southward exodus usually falling in October. Many of the lucky monarchs were able to hitch a free ride on the southward-moving front.

A population of monarch butterflies can migrate up to 3,000 miles south to the Sierra Madre Mountains, embarking on a trip they have never been on before with remarkable precision. The journey can take up to two months, with individual monarchs flying 50 to 100 miles per day.

Once spring rolls around, they return in droves to the United States and Canada. According to the U.S. Forest Service, no butterfly lives long enough to complete the entire migration. Instead, it takes 3 or 4 generations of reproduction after departing Mexico for the butterflies to make it to the U.S. Northern Tier or Canada.

How do we know these were butterflies (dragonflies, and other bugs) on radar? Two ways.

For starters, dual-polarization radars send out horizontal and vertical pulses of radiation. Depending on how the two returned signals compare, we can draw inferences as to the shape of whatever bounced the radar beam back.

In the case of the Saturday’s butterfly front, the shapes detected by radar proved to be a bit wonky — not in line with the more uniform shapes expected from precipitation. With that information, we can surmise that whatever was in the air was biological in nature.


Anything red represents rain. Blue indicates more unusual shapes, often biological in origin. Notice behind the "butterfly front" the large spattering of blue. That's where the insects were. (GR2 Analyst)

“I was here the weekend,” said Bruce Thorem, a meteorologist at the National Weather Service in Norman. “It definitely seemed like one of the better signatures.”

Thorem added that the north wind helped the butterflies migrate south.

Folks along and west of the Interstate 35 corridor in Texas may enjoy a couple of orange visitors in the breeze in the days ahead.

The unusually strong return signature on the radar, commensurate with what would be seen from heavy rainfall, also suggests that whatever the beam hit had a large cross-section. Butterflies and dragonflies seem to fit the bill.

How else do we know that butterflies were among the insects caught up in the breeze? Pictures! Check out the magnificent creatures’ journey below: