Ladybugs are gathering again at the UC Botanical Garden. They do this every fall, and then they disappear. I don't know whether they move on or whether they hide in the duff, but the aggregations only last for a few days, so enjoy them while you can.
Ladybug have bright colors, which is called warning coloration. Have you ever picked up a beetle and gotten yukky stuff on your fingers? They exude a toxic substance from between their leg joints. Birds usually only eat them once; they remember those bright colors and find something else to eat.
Ladybugs eat aphids and other soft-bodied insects as both immatures and adults. Sometimes they eat a little pollen or nectar, but they are not a threat to any plant. This particular ladybug, Hippodamia convergens, occurs across the US and into Canada and Mexico. In California, it has a complicated migration pattern, which is described here at this website: