Brown Marmorated Stink Bugs (Pentatomidae - Halyomorpha halys)
Brown marmorated stink bugs are a very invasive species. It was introduced from Asia in 1998 and is found in most states, including California. They are brownish in color on top and bottom and various markings of gray, white, blue and black. They feed on and do a lot of damage to a variety of fruits and vegetables, including soybeans, green beans, peaches, apples, raspberries and others. In the fall they will sometimes move into homes to spend the winter. They are pretty foul smelling, but don't cause any damage in homes.
They congregate in huge numbers on some plants and they have no natural predators in America, so they do quite well.