Popular wisdom has it that they are thick from Mother's Day (or Father's Day) to the Fourth of July. I have found this to be generally true. The deerflies come after the black flies. Deer flies are easier for me to deal with. They are bigger and slower, thus easier to evade. Funny thing: cats don't seem to be harassed by black flies. Lucky them.
I am beginning to collect some desktop photos that I have made of flowers I have photographed. Please use them freely if you wish. The sizes are marked in the titles. I know I have a lot to learn about this, so please advise me if needed. I am only using photos that are still clearly focused and crisp when enlarged. They can be seen at my Desktop Photos Set on Flickr.
Here are two examples: