Why Did Millions of Ladybugs All Migrate at Once?

What at first appeared to be a rain cloud above Southern California on the National Weather Service’s (NWS) radar June 4 turned out to actually be a huge swarm of ladybugs flying south.

How huge? The swarm, aka “bloom,” of ladybugs appeared on radar to be 80 miles by 80 miles wide, flying about a mile above the ground. The swarm was actually about 10 miles wide at its densest — which is still pretty amazing.

Meteorologists with the NWS were puzzled when they saw a rain cloud on an otherwise clear evening with no storms in the forecast. “But on our radar, we were seeing something that indicated there was something out there,” Casey Oswant told NPR.

To determine what the mysterious cloud was, meteorologist Joe Dandrea contacted a weather observer in the San Bernardino Mountains and asked him to describe what he was seeing in the sky. The observer said it didn’t appear to be a dense cloud but “little specks flying by,” Dandrea told the Los Angeles Times. Those specks were ladybugs.

Why were so many ladybugs flying over Southern California that evening? My first thought was that maybe their houses were on fire, like in that disturbing old nursery rhyme. (It’s wildfire season, after all.)

Fortunately, that wasn’t the case. They were probably convergent lady beetles (Hippodamia convergens) migrating from California’s valleys up to the mountains, where it’s cooler in the summertime, Cornell University entomologist John Losey told NPR.

There were likely so many of them due to a rare concurrence of what Losey called the “cues” that determine what makes these ladybugs move: food resources, weather temperature and the length of the day. Somehow “the combination of cues must have all sort of synchronized so that they went at a very similar time,” Losey said.

Could climate change, or the climate change-related devastating wildfires in California last year, have something to do with it? Losey isn’t sure if global warming is “condensing when they all are going to fly,” he told NPR.

The good news is that the size of that swarm could be an indication that the population of these ladybugs is thriving. They have been in serious decline in the United States, largely due to invasive Asian lady beetles that were brought here in 1916 in an effort to control aphids and other pests in greenhouses without using pesticides. But this solution backfired when those invasive beetles escaped from the greenhouses and spread all across the U.S. as well as Europe. A 2013 study discovered that Asian lady beetles have tiny parasites that infect and destroy native species, eliminating their competition for food.

Along with those Asian lady beetles being really bad news for ladybugs, the downside of that huge swarm could be that “something is affecting their phenology in a way that could put them out of sync with where they need to be safe and where they need to find prey,” Losey said.

One scientist, desert ecologist James Cornett, has doubts that the mystery cloud was really ladybugs. He told the Desert Sun a swarm that size would’ve darkened the sky over the region and prompted “unbelievable numbers of telephone calls to the police.”

While it’s not unusual for large swarms of ladybugs to migrate this time of year, Cornett said the numbers are in the thousands, not millions. He said it’s also strange for ladybugs to be traveling south this time of year, when they normally head up north to find more food.

Cornett pointed out, however, that he’s not the last word on ladybugs. “The world must be coming to an end,” he told the Desert Sun.

Let’s hope not.

Photo credit: Wikimedia Commons

72 comments

Leopold Marek
Leopold Marek2 days ago

Tyfs

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Leopold Marek
Leopold Marek2 days ago

Tyfs

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Virgene L
Virgene L2 days ago

Did anyone actually "catch" a ladybug? Did no small airplane check it out? At any rate, if ladybugs, they were hopefully going to a higher elevation and home. "Lady bug, lady bug fly away home. Your house is on fire and your children are gone."
According to other lore, farmers recite the rhyme to save the insects who do them this service before setting fire to stubble fields. So cool. Thanks.

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Melanie St. Germaine
Melanie S3 days ago

So awesome!

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Ingrid A
Isabel A3 days ago

very interesting

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lori Gearhart
lori Gearhart3 days ago

thank you

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Toni W
Toni W4 days ago

TYFS

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Toni W
Toni W4 days ago

TYFS

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Julia R
Julia R4 days ago

Interesting story! I wonder if the swarm was really ladybugs. I never knew that they would fly in a large group together like this.

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Janet B
Janet B4 days ago

Thanks

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