Gardening: Shoo flies – The cause, concern and potential

Eileen Ward

Recently we had another outbreak of little black flies, especially along the beaches. These are called shore flies and they are a new nuisance for us on Marco Island.

My theory on where they are suddenly coming from is the new ditches that were carved out of our shoreline and beaches when we had our mini-tsunami in January of 2016. It is actually called a meteotsunami and was caused by a fast-moving weather system with squall lines. These air pressure disturbances can generate waves that travel at the same speed as the overhead weather system. This causes a sharp rise and fall in the water levels from the Gulf of Mexico.

To reduce shore fly numbers, eliminate algae, avoid over watering, and limit fertilizer run-off.

As this storm slammed our shoreline water levels rose to more than seven feet and then dropped off to normal after the wave passed.

The reason I know we had these ditches carved from the beaches on Marco Island is because I handle the grounds maintenance for the Duchess and Prince Condominiums located on the beach. That winter we started to get many complaints from the residents that their paths to the beach were flooded with two- to three-feet of water in two places. It became a major issue and we had to fill these low spots to bring the path level back to normal. However after a rain the water remains in the ditches on both sides of the elevated areas created for the pedestrians.

Shore flies have been more of a pest for greenhouses where they use hydroponics and where warm wet conditions exist. Their food of choice is algae for both the immature and adult flies. And the ideal temperature for reproduction seems to be between 70 and 80 degrees Fahrenheit. We now have the perfect conditions for breeding shore flies along our beaches. We have the wet areas from the rain which stands in the ditches. Our temperatures average between 70 and 80 degrees. And then the algae begin to grow from the warm, wet conditions. So the shore flies now have all they need to reproduce in nuisance numbers during the height of season.

What can we do? When I found out algae was a needed part of the life cycle I went to the beach and lo and behold there was a huge mat of algae stretching along these tsunami ditches. I collected some and sent it off to the University of Florida Fort Lauderdale Research and Education Center to Dr. H.Dail Laughinghouse and Dr. William Kern Jr. at the suggestion of our local Dr. Doug Caldwell. They will analyze the algae to see if it contains fly larvae and if so identify the type of algae and type of fly we are dealing with here on Marco Island. And then, if possible, we will try to find some form of control. It is a natural area along the dune conservation areas so chemical control is more than likely out of the question. But perhaps there are some biological controls or a larvacide for the flies that could be used, or something to control the algae. And another idea would be to regrade or fill in the beach dunes to get rid of the trenches that formed and take the soil grade back to its natural level to prevent the water from standing and the algae from forming.

We will have to wait to see what they find and take it from there. One thing is for sure. These flies are a real nuisance economically for the beach front hotels and restaurants. When they appear it is in great numbers and while they don’t bite no one wants 20 plus flies landing on them while trying to have dinner or soak up the sun. But as Dr. Kern said in an email, it may be time to manage expectations and let the public know to expect this influx season of shore flies similar to the love bug season.

I’ll keep you informed.

Eileen and Peter Ward have owned a landscape and lawn maintenance company for 35 years. Eileen can be reached at or 239-394-1413.