Mistake one: treating the flies you can see
The visible adults are the least important part of the population, and every hour spent on them is an hour the actual problem keeps running. Here is why. The University of Missouri Extension reports that a single female can lay around 500 eggs, and that a freshly emerged adult is mating about two days later. So at any given moment, the flies in the air represent a fraction of what is in the drain, in the fruit, or under the appliance. A spray can reduce the count in a room in minutes and change nothing about the trend. The University of Kentucky puts the full cycle at about a week under favorable conditions, so you will see the replacement wave inside eight to ten days. The correct sequence is the opposite of instinct. Find the fermenting material first. Remove it. Then, if you want a clear room tonight, use a light aerosol as the last step rather than the first. In a South Dakota kitchen running a furnace for five or six months, the conditions never turn against the insect, so nothing about waiting works in your favor.
Mistake two: searching only the kitchen
The kitchen is the obvious place and often the wrong one, particularly in this state. South Dakota's short growing season delivers a lot of produce in a few weeks, and most households do not keep it on the counter. It goes to a basement shelf, a back entry, an unheated porch, or an attached garage where the temperature is convenient. Those places are checked far less often than a fruit bowl. The other overlooked areas are the wet ones. A basement floor drain that dried out, a laundry tub used twice a year, a utility sink, a sump area, a refrigerator drip pan in a garage. With outdoor humidity around 69 percent and dry winter air, these interior wet spots carry the entire load, because nothing else stays damp. The way to search efficiently is to let the flies tell you. Put a labeled trap in the kitchen, the basement, the entry, and the garage. Count after two days. The heaviest jar defines a search radius of a few feet, and you can stop guessing about everywhere else.
Mistake three: pouring something down the drain
This is the most common wasted effort in the whole problem, and it fails for a simple mechanical reason. The material that feeds larvae in a drain is a film clinging to the inside wall of the pipe, usually within a few inches of the opening where air and organic matter both reach. When you pour bleach, hot water, or a commercial drain product in, gravity carries it down the center of the pipe. It touches the film briefly at best. What works is contact. A stiff bottle brush or a drain brush run around the inside wall physically strips the layer off. Follow that with a foaming enzyme or bacterial product, which expands to fill the pipe and holds contact against the sides for far longer than a liquid can. Test whether the drain is even the source before you spend the effort. Cover the opening overnight with clear tape, sticky side down. Flies stuck underneath in the morning came out of the pipe. A clean tape and a full counter trap sends you back above the sink, where the answer is food rather than plumbing.
Mistake four: deciding after three days that it failed
People give up on the right approach constantly, because the timeline of the fix does not match the timeline of their patience. When you remove the breeding material, the adults already flying are unaffected. They live on for days. More importantly, the larvae that already left the food to pupate are sitting under the dishwasher or along the toe kick, and they will emerge on their own schedule. The University of Maryland Extension notes that larvae feed five to six days and then crawl to a drier spot, and Missouri Extension puts emergence to mating at about two days. Add those up and you get a tail of new adults appearing for well over a week after your kitchen is spotless. So set the expectation at fourteen days and measure instead of guessing. Write trap counts down every second day. A line that trends downward, even unevenly, means you found it. A line that stays level for ten days means you did not, and that is the moment to widen the search or call somebody, not on day three.
Mistake five: expecting winter to solve it
In a state where the median winter low is around 7F, it is reasonable to assume the cold will handle a small insect. It will not, and this misunderstanding costs South Dakota households entire winters. Cold ends the outdoor population completely. That is real. But an indoor population has no relationship with outdoor temperature. Your kitchen in Aberdeen in January is warmer than a July porch in a mild climate, and it stays that way continuously for months. The practical consequence is that winter is actually the best time to solve this, not the worst. Nothing new is arriving. Every fly in the house came from a source in the house, so the search is closed and finite. Find it once and it does not get resupplied until spring. Use the season deliberately. Brush the drains, wash the containers, check stored produce, refill unused floor drain traps, and empty the refrigerator drip pan. A January afternoon spent doing that in a Watertown or Rapid City home clears the ground before the next round of grocery-borne eggs shows up in the spring.