5 steps to figuring out ‘phantom phorids’ — and what to do next


November 5, 2019

Photo courtesy of, and copyrighted by, Gene White, pmimages@earthlink.net

Photo courtesy of, and copyrighted by, Gene White, pmimages@earthlink.net

Peanut butter and jelly. Peas and carrots. Bacon and… well, anything. Allow me to submit: Food and Phoridae.

Phorids are small, humpbacked flies that lurk in the nightmares of even the best pest control technicians, and can cause health inspector shut-downs, third-party audit failures and endless callbacks at clean facilities. They’re enough to drive you nuts — or at the very least, envy the guy who spins a billboard on the street corner while wearing a Statue of Liberty costume.

Phorids can strike at facilities as small as a coffee shop or food plants as large as a football stadium. No matter what the size of the business, they will cause both you and your client headaches. Phorids can quickly reduce you from a respected contractor to nothing, and it is not fair. Even though it can be a long and sometimes lonely road, keep your chin up, because there is a solution and finding it is extremely rewarding.

Keep it simple, stu…dent

Phorids always are caused by one thing: decaying organic material. Find that material, throw it away and the problem resolves itself in a week or two. Never forget that.

However, sometimes the material is not visible. Sometimes what is causing the infestation lies below the surface in the substrate under the floor.

Here are five signs your phorid problem may be lurking below the surface:

  1. You capture thousands of small-sized phorid flies minutes after changing glue boards in insect light traps (ILTs).
  2. There is no particular location where the phorid flies are concentrated.
  3. Neighboring rooms or neighbors (in multi-tenant facilities) complain of “small flies.”
  4. Flies persist, no matter how clean the facility.
  5. Multiple calls come in from the same facility each week.

So, what do you do when the source isn’t something you can immediately show your client?

First, don’t panic. Realize that the solution may take considerable time, and that you need to be the confident expert that you are who knows what your client needs. Second, don’t make it more complicated than it needs to be.

Ask yourself and your client, “Is there organic material at this facility?” Of course there is, or you wouldn’t have phorids. Now it is time to find out where the organic material is decaying. You will need your detective hat, a flashlight and knee pads, but this is certainly something you can do.

You cannot provide an effective integrated pest management (IPM) solution without a proper inspection. However, an infestation in the substrate below the floor requires different inspection tools and techniques. Here are some approaches that have been effective in identifying the source of an infestation when it lies beneath the surface:

  1. Your first course of action should be inspecting above ground for clues. Inspect for cracks, gaps and holes along the baseboards and floor, both inside and adjacent to the area with the active population. This may include an inspection of water drainage on the exterior of the building.
  2. Interview your client to determine the history of the sub-floor. For example, a facility I inspected had an abandoned sewer crock buried below the floor, which no one currently working there realized until they checked their records.
  3. Have a licensed plumber scope all drain and lateral lines for cracks or collapsed lines. Be aware that drains travel throughout the facility, and a collapsed line may originate in a different room. The facility may provide a plumber, or you may subcontract one for the facility.
  4. A more aggressive approach, suitable before a client begins a large capital expenditure, is to have the facility or another contractor drill holes through the substrate using a grid pattern. Then set monitors over each hole to determine, for certain, that the phorid flies are below the floor. Be aware that the substrate can be as deep as 2 feet below the floor in some concrete structures. You will need to be careful to protect the monitors from water and above-ground phorid flies, which can create bad data. After several hours of monitoring, inspect the monitors and record the information. Chart it on a map to present to your client.
  5. Use all the data collected to determine the most probable location of the contaminated soil.


The solution is in the soil

Once you have found the contaminated soil, the solution is to excavate it all. The problem will resolve itself by month’s end. Fortunately, it is that simple. Unfortunately, it is that simple.

By this time, you have been an excellent detective and you have provided your client phenomenal service, but you have made no money in the process. That’s OK, it is your job. But it isn’t over, and this is where the difficult part comes — convincing your client (and an army of well-dressed people you never knew existed) to demolish beautiful tiled floor to remove all the wet or contaminated substrate. You’re going to have to contend with the director of buildings and grounds, the VP of facilities, the general manager, the plant manager, the corporate quality assurance director and everybody in between. Don’t do it alone!

Save the date

After letting your direct contact know the solution is going to take considerable work to excavate contaminated soil below the surface, be proactive by requesting that you meet with any decision-makers at the facility who would be needed to make such a repair happen. Believe me, you are going to meet with them anyway, so do it on your terms.

Then, match the title of the client’s company officials with your own. If the client’s regional manager is going to be present, ensure that your regional manager (or equivalent) is present as well. If you have a technical director, this would be a great opportunity for him or her to show off what they know.

The truth is that your direct contact at the facility probably trusts and respects you deeply; however, any accountant, VP or director faced with tens of thousands of dollars of repair work and major disruptions to production in their facility, most likely will not have that same level of confidence in you.

So, when you meet, knock their socks off. Prepare with your team beforehand and put together a powerful presentation. Use Keynote or PowerPoint presentations with pictures — of their own facility, if possible — to show them the biology of phorid flies, the root causes of phorid flies, and your inspection and research data you collected from the facility. Stress to the group that the only solution is to remove all of the “contaminated” soil. And be sure to use the word contaminated. Not only is it the proper word to use, it works.

Contaminated soil

So why are phorids in non-food areas?

When contaminated water is introduced to the substrate, not only does it provide harborage for phorid flies, it adds to the natural settling that happens to a building after construction. As a result, the soil will compact and create gaps and galleries throughout the substrate that will reach far past the source of soil contamination. Keep in mind that just a quarter-inch gap may seem insignificant to you, but it appears like a 15-foot-tall warehouse to a phorid. This space is why you can find phorids throughout the facility when the source is localized to food areas.

The word “contaminated” can be alarming at first. However, instead of thinking about arsenic, oil spills and hazmat suits, realize that we are talking about a suitable environment for phorid flies to breed. In other words, soil that has actively decaying organic material. A better phrase might be “dirty soil,” but who is going to call dirt “dirty?”

This begs the question, “How did my client’s soil get contaminated?” The truth is that your client is contaminating its soil. It happens whenever water created or used in the facility has a path to escape below the floor instead of through proper drainage channels. Steam that is created, tools that are rinsed and floors that are washed all need a properly sealed structure and intact drainage system to escape if you are going to prevent soil contamination. Again, phorids only exist when decaying organic material — aka, water mixed with organic material or contaminated soil — is present.

Sweet success

If you succeed in navigating your client through this process, you and your company will have a great sense of accomplishment and be treated as heroes, just like Batman and Robin, Holmes and Watson, Lennon and McCartney, or Bacon and … well, anything.

BLAHNIK is field training manager for Milwaukee, Wis.-based Wil-Kil Pest Control and Holder’s Pest Solutions. He may be reached at ablahnik@wil-kil.com.


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