When was the last time you inspected the vents in your Gabled Roof? Older homes in this area of Northern California, in many cases, have large openings in the 'Gables' to allow for ventilation. Some are very ornate.
These openings in the Gabled end of your roof should be covered with screen on the inside to prevent insects, bats, birds etc. from entering the attic area. The screen will also prevent small rodents from entering your attic via a tree located close to the opening.
Take a look in the attic, if the opening is not screened, take some measurements and head to the hardware store. Screen is usually available by the foot. You will need a staple gun to install it. Roll the screen over for about one inch along the edge to make sure the staples will secure it tightly. Staple the screen about every six inches.
You will still have good attic ventilation but without the insects and their larger friends.