Did it look like this?
Could be some type of cabbage moth caterpillar. If you've seen those white moths getting about most likely is.
The little pricks are fast workers and ripped through my broccoli in a couple of days.
I launched a counter strike with tomato dust which sorted them out but I don't know if that would be suitable for hops. A good, fairly benign method for control is steeping some garlic and chili in water for a few days, pouring it into a squirt bottle with a few drops of detergent. They hate it.