If you've ever gotten particularly lucky during a winter hike in the hills or mountains, you'll have stumbled across this spectacle. Thousands, even tens of thousands of ladybugs, crawling over each other in one huge clump. It's called an aggregation, and it's something these usually solitary beetles do each winter from about November to February.
According to KQED Science, "Scientists believe the behavior evolved as a way for a solitary species to reproduce and to cope with a limited winter food supply. After fattening themselves up, and before bedding down for winter, these ladybugs are getting together to take care of some final business — namely, mating ... Within the ladybug clumps, the movement is scrambling and unpredictable, not hierarchical as it is in a beehive or ant hill. Scientists think that the females — about half of the population, all of them previously unmated — may be selecting mates amid the chaos."
Here's a great video that shows what these aggregations look like and explains the science behind them:
Ladybugs are important beneficial insects to have around as they prey on aphids, an insect that can destroy gardens and crops. These red beetles are our best friends for healthy plants. Unfortunately, they seem to be in decline. You can help scientists keep track of the species' status by participating in a citizen science project called the Lost Ladybug Project.