The Spider hitch is an excellent knot for quickly forming a double line when light tackle fishing, although it's not as durable as either the Bimini twist or the Australian plait which we prefer for heavy tackle applications.
To Tie a Spider Hitch:
Double over the line and form a reverse loop.
Hold the reverse loop between your thumb and forefinger.
Wrap the doubled line around your thumb and the reversed loop five times (15 times if using superbraid). Then pass the end of the double line through the reverse loop. Slowly pull on the double line allowing the loops to unwind off your thumb.
Moisten with saliva and pull evenly on all four ends to tighten.