Small Flies, Big Problem

We were recently contacted by a commercial customer about a small fly (phorid) problem that spontaneously exploded. This dramatic increase in flies had infested every floor, every office and every life throughout the building. It was a problem without a solution.

INSPECTION. Considering the basic premise of an IPM program is to do a facility inspection, we set off. As any respectable pest inspector would do, we started in the basement with the drains. There was standing, stagnant water in the drains and flies were in the area — some even resting on the grates of the drains. The obvious source, right?

Being noble and not trying to look too smart too quickly, we moved on and progressed up the floors. The first floor was worse than the basement, and the second floor not as bad as the first. Hmm. Now, in my head, I’m thinking, “Shouldn’t they be worse near the source? There must be some dry trap coming up from the basement that is giving free access to the upper levels, and that’s why they are worse on the first floor.”

The drain quest commenced on the first floor, and not a single problem could be found. No source on the first floor seemed reasonable. We thought it must be the drains in the basement. The upper floors were not as bad. It seemed that there was an issue between the basement and the first floor. Now, how do we start eliminating possibilities?

THE PLAN. First off, we knew we had a drain issue, source or not. If water was backing up and not draining, we could have a variety of problems going on down there — cracked pipes, blockage, ninja turtles, who knows! The only way to know is by sending a scope down the drain and looking. This is best completed by a plumber, so a recommendation can be made to remediate the problem. A recommendation to scope the drains was made, and that was scheduled.

In the meantime, the drains were emptied by pumping the water out. No stagnant water, no flies, right? Wrong. Flies continued to increase in the building.

Now what, you may ask? Monitors, that’s what.

Temporary insect light traps were placed everywhere. They were checked daily. To give you a sense of the scale, in one office, more than 500 phorid flies were captured overnight. Within a couple of days, it was obvious that the issue was worse in one area of the building — near the loading dock.

You see, this facility had been receiving large amounts of deliveries due to furniture being changed out in parts of the building. Doors were being propped open for long stretches of time, and dumpsters were right outside the doors. The construction dumpsters were getting a fairly large amount of food debris from worker lunches, and they didn’t have lids. These dumpsters were covered in phorid flies.

In checking the airflow of the building, it was determined that there was negative pressure inside. When the doors were open, the air was being pulled in from outside, basically sucking the flies in all day.

SOLUTIONS. There were several ways to go here on recommendations and solutions. First, the issue could have naturally resolved itself when the furniture delivery was complete. However, that could take a while and wasn’t a great solution in the short term.

Keeping doors closed would help but was still going to let flies in when they opened. One of the best options was to move the dumpster. Getting it away from the doors would take the breeding site away from the entry point. Adding an air curtain to the door wouldn’t hurt, and making a few of the insect light traps by those doors permanent might help collect what got through the air curtain.

As for the drains, we’re still not sure. Ongoing investigations into why they weren’t draining properly continue, but it likely isn’t the source we initially thought. I’m glad we didn’t stop there. Maybe it is ninja turtles!

The author is technical services director at Rollins in Atlanta.