A swarm of motorbikes

On my way home this afternoon, in my newly fixed car (!), I saw something I've never seen in that way before. I spotted them first as a bright trail of lights emerging over the hill in front of me down the opposite carriageway. It took me a second to register as to what they were! The bright lights of a long parade of motorbikes.. and they kept coming! I trailed along behind a lorry at 50mph because I was just enjoying watching them so much. It was overcast and fairly dark for that time in the afternoon, which made their lights that much brighter. There must have been over 100.. a continuous stream. I wonder where they were all off to?

Is there a name for a group of motorcycles?