I LIKE Killing Flies

I LIKE Killing Flies!

My wife owns a bakery and as you know, flies and restaurants do not mix. Hence the title of this month’s musing on all things natural and sustainable, “I LIKE Killing Flies”.

Did you know that all insects “breathe” through their bellies? Their abdomens are coated with an oily substance that helps their spiracles or air holes to pull oxygen out of the air and expel carbon dioxide. Air travels throughout the insect’s body through a tube-like ventilation system to get to the cells. 

And therein lies their fatal kryptonite weakness. Soap washes away oil and thus it attacks and kills insects four ways.

First, it dissolves and washes away the oils that protect the insect’s spiracles, immediately disrupting their respiration. Many high metabolism flying insects like wasps drop immediately upon contact with soapy water at the appropriate dilution.

Second liquid soap gets sucked up into the insect’s trachea where it then comes into direct contact with various cells and structures. Once inside the body of the insect, soap acts on the fatty layers of these cell membranes, dissolving them and causing the cells to spill their contents and die. This is similar to what happens when you wash your hands.

Third, soap dissolves the exoskeletons of many insects. 

And fourth, as the soap dries it coats and clogs up the spiracle holes, disrupting respiration.

In many ways, soap is the ideal insecticide. It is completely safe and nontoxic to mammals and most plants are unaffected by it at standard concentrations. While soap usually kills adult insects very quickly, it does not always destroy the eggs, meaning that it is very common to use 2-3 spray soap treatments over a week to turn the tide on a garden insect infestation. 

Start with the best 16oz spray bottle you can find. You want a trigger type sprayer for outside and plate glass use. You can transfer some into a 4oz bottle with a button sprayer (not a trigger spray) for occasional inside use.

Fill your 16oz bottle ¾ with warm water, and add castile (preferably locally made) liquid soap

Screw the sprayer on tightly, and turn upside down and right side up several times to mix. Then wash off the outside with soapy water on the bottle for a better grip. 

For Med flies, gnats, no see-ums, and other soft-bodied insects, add 1oz of castile liquid soap. A shot glass works great for measuring. These insects can be taken down while circling with a fine mist sprayed above them that filters down onto their bodies. 

For cabbage worms and general garden pests, start with 2oz of soap per 16oz bottle. These will need a direct hit to take them out. Adjust the sprayer so that it is neither a wide mist nor a single line of fluid. You want to give yourself a roughly 3-inch splat area for coverage. The insect must be completely covered in soap water to be effective. 

For house flies, cluster flies, “Japanese” beetles, and larger insects, use 3oz of soap per 16oz bottle. Add another shot if they seem resistant to the spray. 

A few plants like tomatoes becomes more sensitive to light damage after being sprayed with soap solution. It is a good idea to do a whole tomato plant spray treatment, and then rinse the leaves off a half-hour later just to be extra safe. Castile soap will not harm your garden and improves soil permeability to water in dry conditions. It is potassium-based, which is a necessary plant nutrient. 

The beauty of this system is that if you notice your solution is not strong enough for a certain critter, just add more soap. There is a limit at which your sprayer will not work properly. If that happens slowly add more water to the bottle and squeeze out some of the foam on top.  

Clean up by carrying a cloth or paper towel with you to wipe off excess spray soap. You are literally cleaning surfaces as you purge your space of the demon invaders. Clean large plate glass windows with 1/2 shot soap spray and a squeegee or paper towels. 

You can say goodbye to toxic organophosphate insect sprays and use organic soap instead!

Now that’s a foaming success story!


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  1. Marian Lizon on August 31, 2020 at 4:38 pm

    Great idea ,I love it. If you come up with an equally great idea to keep squirrels from stealing your tomatoes I would love to hear it. ❤

  2. Ken Kozick on August 31, 2020 at 7:48 pm

    That was a fun read!