At first, meteorologists at the Weather Service’s San Diego office didn’t know what they were looking at.

“We were trying to figure it out ourselves,” said Mark Moede, a meteorologist at the office. “It looked like echoes reflecting off raindrops, but we weren’t seeing any clouds.”

Moede said the office called one of its volunteer weather observers in Wrightwood, Calif., where the radar displayed deep shades of green. The observer reported “ladybugs everywhere.”

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Based on this report, the Weather Service tweeted that the radar signature came from “a cloud of lady bugs."

But in an interview, Moede added a caveat to that explanation. He cautioned that the swarm was so big that “it does raise the question of whether it could be something else.”

He said it’s possible the radar was displaying chaff, bits of aluminum dispersed by the military to fool and overwhelm radar signals that may be tracking aircraft.

In December, a mysterious radar signature appearing over Illinois and Kentucky turned out to be chaff.

But massive swarms of bugs have been picked up by radar before. In July 2014, radar revealed a “bug derecho” from “an epic Mayfly hatching event” in Wisconsin.

Other non-precipitation things routinely sensed by weather radar include bats, birds, butterflies and wildfire smoke.