Big Bug - Anyone know what it is?

Hi everyone,
I was looking through my photos and saw photos i took of this enourmous (almost 4 inch) flying bug. It was mid/later summer along the coast in san diego. Any ideas? is it nasty or good? what should I do if i see it again?

Thanks
Mitch

I have no idea what it is but if I saw a 4 inch bug like that I would grab a can of Raid, spray and run! I remember the first time I saw a mud dauber (kind of a wasp I believe)I was terrified. Then we saw crazy huge yellow and black spiders in Iowa. Freakish like a horror movie.
Definately the worst aspect of gardening. Bugs and creepy crawly things.