Mar 17, 2012 – Flies, Gnats, and Moisture
QUESTION:
I have an office building that has Phorid Flies and Fungus Gnats hovering at the entrance (outside). There is a lot of landscaping around the entrance but no grass. There is no evidence anywhere else around the building. We've tried a number of products but can't seem to get them under control. What else can I do to solve the problem and will drying out the landscaping help? Thanks.
ANSWER:
Let's appreciate, first of all, that the flies seem all to be on the outside. These kinds of flies in number indoors suggest a breeding source inside that at best may be hard to find and at worst could represent some serious plumbing problems. This time of year when the weather begins to get warmer is when all of those living creatures outdoors that have survived the winter begin to get active again and do what they are meant to do - grow, breed, and create more of their own kind. Phorids and fungus gnats are certainly common insects outdoors, and they still breed in their early stages in the same kinds of micro-environments as they will inside - damp places where their foods of fungus, molds, algae, and other decaying plant material are available.
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I have an office building that has Phorid Flies and Fungus Gnats hovering at the entrance (outside). There is a lot of landscaping around the entrance but no grass. There is no evidence anywhere else around the building. We've tried a number of products but can't seem to get them under control. What else can I do to solve the problem and will drying out the landscaping help? Thanks.
ANSWER:
Let's appreciate, first of all, that the flies seem all to be on the outside. These kinds of flies in number indoors suggest a breeding source inside that at best may be hard to find and at worst could represent some serious plumbing problems. This time of year when the weather begins to get warmer is when all of those living creatures outdoors that have survived the winter begin to get active again and do what they are meant to do - grow, breed, and create more of their own kind. Phorids and fungus gnats are certainly common insects outdoors, and they still breed in their early stages in the same kinds of micro-environments as they will inside - damp places where their foods of fungus, molds, algae, and other decaying plant material are available.
A dry environment is quite unacceptable to these flies, so if there is anything you can do to help eliminate wet areas outside it will be helpful in reducing the flies. If there are layers of thatch in the lawns this could be a breeding area, as is a thick layer of wet mulch over the soil. We love to cover dirt with other materials here in California, but this does tend to keep the soil damp and if it is leaves or bark that we use for that cover it also provides the food ingredients for the fly larvae. Exactly why the flies are choosing the entrance door for their hangout is hard to say, other than it may be a covered, shaded alcove that attracts them for a resting spot. Perhaps it also signals a source in that immediate area where the flies are breeding and the adult flies are emerging from. Fungus gnats are not particularly strong fliers, so they would look for resting places where there is not much wind.
If the presence of these adult flies is particularly annoying to the employees or their clients at this building you could do some things to help reduce their numbers. You might apply a residual insecticide to the walls within that entry way, but this should be considered only as temporary relief. Fly problems are nearly always best approached by source management and eliminating the conditions that are creating the flies to begin with. Do an inspection of the exterior to note in writing all those things that should be addressed. If low areas allow water to settle they can be filled. If irrigation is excessive or sprinklers are not functioning properly that can be fixed. Any accumulations of plant debris should be removed. Anything that can be done to reduce standing moisture and remove food resources will help stop the production of the adult flies.
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