Really neat interaction showing off their role as secondary pollinators. Altogether I saw two rattlesnakes and a bullsnake in the span of an hour. This was at the edge of a large black-tailed prairie dog colony in the foothills of the Rockies. I missed the strike by a couple minutes but you can see how big the fangs are in this photo. Both are fairly large adults.
That's still pretty huge compared to adders which max out at around 80cm for females. Grass snakes, the only other type of snake found in mainland Finland typically grow to be around 75-90cm long so those are some pretty big snakes you have there