Painted lady butterflies are arriving in droves in southern California as they make their annual migration northward, and their arrival is a delight to many.

It's also a reassuring sight to scientists who worried that the migration would be sparse this year. They have desert rains to thank for the surprising population boom.

"The conditions were perfect for them, so now we are seeing a lot of them coming out all at once," Doug Yanega, a scientist at the Entomology Research Museum at the University of California, Riverside, told the Los Angeles Times.

Butterfly bonanza

Each year, the painted lady butterflies make an annual migration north from Mexico to summer in the cooler climes of Oregon and Washington state in the Pacific Northwest. Sometimes they venture into Canada and have even been seen in Alaska. These are hardy butterflies that will fly for hundreds of miles. When their fat reserves give out, they breed, die and then the next generation keeps the migration going.

The painted ladies are in a population boom not seen since 2005, when scientists estimated that 1 billion butterflies made their way northward. Lending a hand in their migration is the all the rain California received. More rain, and a very mild February, meant more plants, and more plants meant not only more places to lay eggs but more food for the caterpillars to eat before they become butterflies.

While monarchs are tied to milkweed, painted ladies will eat just about anything. They prefer nettles, mallows and borages, according to the Times, but will devour lupine, sunflowers and other types of plants, too.

And they keep on coming

Provided the weather doesn't get too hot or too dry, the butterflies could keep flocking through California for another three months. That could mean millions of butterflies flying through California.

And that's great news for the butterflies and the people who enjoy seeing them. Jessica, an environmental artist and jewelry maker, caught a swarm of butterflies taking a beach route north along Redondo. That's her video at the top of this file.

Meanwhile, some other butterflies visited Los Angeles International Airport.

The migration brings nature right to people's doors, too. This resident of Julian, California, in San Diego County, calls the butterfly migration "the coolest thing in nature since I've been here; honestly, it's amazing" in the video below.

So if you're out and about in California, even bicycling and driving, soak in the wonder of the butterfly migration.

"They were flying parallel to me, just bobbing along as I rode past the date palms," conservation director at The Living Desert Zoo and Gardens in Palm Desert James Danoff-Burg told the Times. "It was absolutely magical. I felt like a Disney princess."

Painted lady butterflies fill the skies over southern California
Painted lady butterflies are migrating north for the summer, and they're overtaking southern California, to the delight of many.