When I was up in Yellowstone National Park in Wyoming this summer I was observing butterflies with two other people and it was an open meadow in between the woods and you could spot the butterflies from a long distance away hovering above the flowers and vegetation even with your eyes. Most of them were smaller species also. There were many different species. I think it all depends on your habitat.No Dennis you couldn't do this. It is impossible.
Why?
Because there would be too much vegetation in the way to see the butterfly. This happens when you have a 100mm macro lens and you are photographing from only 1 foot (30cm) away so you have absolutely no chance of seeing the butterfly or dragonfly from 18 feet.
I am sure this has been proven by amazing and astounding research and published by the German professors back in the 1920s and a Birdforum member will begin quoting from it any minute now...
Seriously, you would have to be amazingly lucky that there wasn't leaves, twigs, stems, blossoms or fruits or nuts between you and an insect 18 feet away.
Lee