We have found that the yellow flies start on or around Memorial Day and the dog flies start on or around Labor Day. Yellow flies can leave a large swollen area around the bite that lasts for days. We were on the beach Aug.24th and the dog flies were terrible. They seemed to be attracted to anything white, so not sure about being attracted to dark objects...were all over our white bucket, white umbrella pole and husband's white shirt. You just couldn't get out of the water and stay on the beach! Tried Cactus Juice and Cutter but nothing kept them off. Wrapped up in towels and went home.
Here is a recipe from the Walton Sun, May 2004 - I've made up a batch and keep it in a spray bottle in our refrigerator. Seems to work best if you apply right after being bitten. Rub in briskly. You can also try window clearner with ammonia, in a pinch.
Yellow Fly Bite and Sting (Jellyfish) Relief
1 tsp baking soda
1/3 cup ammonia
1/3 twp papain (meat tenderizer)
1 crushed asprin
Mix thoroughly and store in refrigerator. Be sure to label container.
When needed, shake well and apply with a cotton swab -
or heck, just spray it on fast!
Yellow flies seem to like shady, humid areas, tend to avoid large open sunny areas, hence, don't usually see them on the beach. For dog flies, enjoy the beach when there is a Gulf breeze.