On Tuesday evening, around 9.30pm, the US National Weather Service (NWS) in San Diego County picked up an unusual signal on its radar. At first glance, it looked like a raincloud or storm system. But nope, it was a cloud of bugs. Ladybugs, mind you, so not so bad, but still a cloud of bugs.

The collective noun for a group of ladybugs is a “bloom,” according to NWS San Diego who shared the video on Twitter (although a "loveliness" is also listed). 

“The large echo showing up on SoCal radar this evening is not precipitation, but actually a cloud of ladybugs termed a ‘bloom,’” they said.

At first, the meteorologists at NSW's San Diego office weren’t sure what they were seeing.

“We were trying to figure it out ourselves,” Mark Moede told the Washington Post. “It looked like echoes reflecting off raindrops, but we weren’t seeing any clouds.”

According to Joe Dandrea, another meteorologist who was on shift that night, the bug formation appeared to be about 130 kilometers by 130 kilometers (80 miles by 80 miles), flying at between 1,525 and 2,745 meters (5,000 and 9,000 feet). Speaking to the LA Times, he pointed out the swarm wasn’t one huge dense mass, but rather spread out, though he did say the most concentrated mass was about 16 kilometers (10 miles) wide.

When Dandrea saw the signal pop up on the radar, he explained they called a spotter (volunteers at the NWS’s SKYWARN storm spotter program) in the vicinity of the mass, near Wrightwood in the San Bernardino Mountains, to confirm what they were seeing.

“I don’t think they’re dense like a cloud,” Dandrea told the LA Times. “The observer there said you could see little specks flying by.”

However, the next day they had completely disappeared.

So, what was happening and where did they go?

Ladybugs, or ladybirds as they are also known, are pretty common across the world. It’s unclear which species of ladybug caused the radar signal as there are around 5,000 species of ladybug worldwide, and over 100 found in California alone.

Many of these species spend the winter in the Sierra Nevada mountains and then fly to the warmer coasts and valleys in spring to eat aphids, mate, and lay eggs. They likely moved on to somewhere even warmer, such as Mexico.

Moede did point out in his interview with the Washington Post that the swarm was so large “it does raise the question of whether it could be something else.” He suggested “chaff”, bits of aluminum released by the military to confuse radar signals that may be tracking airplanes, as a possible alternative explanation.

However, it’s not the first time a swarm of bugs – or other beasties, for that matter – has been picked up by radar. In July 2014, an epic mayfly hatching event in Wisconsin was picked up by NWS La Crosse. And as you can see in the video below, in July 2015, NWS Norman picked up swarms of grasshoppers and beetles in Oklahoma. In 2016, NWS Memphis caught a large flock of geese, and in 2018 NWS Austin/San Antonio caught a swarm of bats emerging for the night.

So a swarm of ladybugs is not so bad. It could have been much worse, after all.