These are Harlequin bugs, or Harlequin cabbage beetles (Murgantia histrionica). They live by sucking the juices out of cabbages and other cabbage family members. Most of the time they are considered a pest by farmers. They are part of the stinkbug family, although they also play dead when disturbed.
The females lay up to 12 eggs in a double line on the leaves…
After hatching, the young (nymphs) cannot fly. They will go through 5 successive molts before they get the color patterns and the wings of an adult. That takes approximately 42-47 days.They are very dependant on temperature conditions for their growth and development.In northern areas, they only have one clutch per year. In southern areas they can have three clutches. When mating the male and female stand with their abdomens touching, for the transfer of sperm.
These bug pictures were all taken on one Bladderpod bush, a native bush to California. Some harlequin bugs will spend their entire lives on a single bush.