We have tested this product and can vouch for its effectiveness.
As you know, deer flies seem to land on silken feet and give you no warning before they rip out a piece of your carcass. But their motto is: "Those whom the gods would destroy, they first make mad". So, they fly round your head a dozen or more times before landing on the back of it.
If you have one of our deer fly patches on the back of your cap, they will immediately be trapped when they land. The patch will not stick to your fingers, but will still trap the deer flies. It's all small-scale jungle warfare.
Offered in a package of 12 sticky patches, each measuring 2 1/2" × 5 3/4". One patch will stay effective for several days.
Made in USA.