Forecasters working the Tuesday evening shift at the National Weather Service's San Diego office were confused.A large echo indicating rainfall showed up on weather radar over the San Gabriel Mountains near the town of Wrightwood, California, but there were no clouds in the sky."The radar was showing there was something out there," said Mark Moede, a forecaster with the NWS. "We looked at the satellite image, but there weren't clouds that size in the area."A few calls were made to weather spotters in the area, and finally one of them said, "ladybugs!"It turns out a massive cloud of ladybugs, called a bloom, measuring 10 miles wide and 15 miles long, was flying around above 5,000 feet elevation."He said it's an annual bloom that happens around this time of year," Moede said.In California, the beetles are known to winter in the Sierra and gather in huge masses in valley areas in the spring to feed and mate, usually in the same places year after year.Amy Graff is a news producer for SFGATE. Email: agraff@sfgate.com.