Boy are YOU ever lucky ! That is the deaded " Beer Stealing Bug". No wonder it was sitting on the branch. It hangs around your camp keeping a watchful eye on you and then when you;
A) go to the bathroom or
B) pass out, it sneaks in a drinks what is left. They are also strong enough to fly off with your stash ( the reason for the 4 wings... the need the extra lift).
They are also found in the company of the West Coast Barking Spider.
( these you can't se but you can hear them & they give off a very bad smell )