James,
Not to worry. I'd bet you have a big herd of cows nearby and/or hay fields. They love to follow the tractors mowing hay and pick up the bugs as the bugs flee for their lives.
Yes, they do leave their calling cards on my piers, but I never have seen them eat one fish. They will leave soon for Mexico, not to be seen again until next spring...in their place come the water turkeys from the North. Now there is a bird to worry about.
