A hatching caterpillar eats its way out of its eggshell.  If there are pathogens left by the adult butterfly as she laid the egg, the caterpillar eats the pathogens and becomes ill.

monarch egg hatched

To prevent this from happening, universities, research facilities, and breeders disinfect eggs before caterpillars hatch.

Although we have a video illustrating how to disinfect eggs, we realize some of us prefer written directions.

First, eggs can be disinfected on or off the leaves. If you prefer to take them off, allow several hours for the eggs to dry. If the leaves have been picked from the plant, it is more difficult to take the eggs off the leaves. As leaves begin to wilt, they become elastic. As you gently rub the egg, the leaf moves instead of the egg. To prevent this, I wrap a wilting leaf around my finger, holding it taunt, and remove the egg with my other hand. This video illustrates how to remove eggs from a fresh leaf.

If eggs are left on the leaves, be aware that some eggs will come off as they are disinfected. A strainer will be used in the process. The strainer MUST have a very fine mesh, whether it is a kitchen strainer or a piece of cloth/tulle/screen.

The instructions for disinfecting eggs are the same whether the eggs are on or off the leaves.

It is simple and easy to disinfect eggs. If you are nervous, we recommend practicing with dry grits, rice, or other item until you are comfortable with this process.


~ Water
~ 3 containers (one each for eggs, bleach water solution, and rinse water)
~ Bleach 5.6 or 8.25 percent sodium hypochlorite (plain ordinary bleach, no scented/splashless/whatever)
~ Measuring unit (Tablespoon, measuring cup, teaspoon, whatever)
Fine strainer
~ Clock or 60 second timer
~ Paper towels (2)
~ Eggs that have dried for at least 2 hours, preferably overnight

1. Fill a container almost full of water. (You’ll use this to rinse the eggs at the 60 second mark.)
2. Measure out a mixture of 1 part bleach to 19 parts water if your bleach it is regular bleach, about 5.6% sodium hypochlorite. If your bleach is around 8.25% sodium hypochlorite, mix 1 part bleach to 32 parts water.
3. Place eggs (either on or off the leaves) in a container.
4. Set the timer and …
5. … immediately add the bleach/water solution to the eggs. DO NOT add eggs to the solution. (**We explain why below.)
6. Gently stir or agitate the solution with the eggs.
7. At 60 seconds, pour the solution/eggs through the strainer and instantly place the strainer with eggs in water. (***Bleach should be diluted/stopped instantly as close to 60 seconds as possible.)
8. After at least 60 seconds, remove the eggs from the rinse water and place on a paper towel to dry. Cover the towel so pathogens in the air won’t land on and stick to the eggs.
9. After the eggs have dried (normally within an hour) place the eggs in the container of your choice for hatching. Some people place the whole paper towel in the middle of a plant. Some place the eggs in small cups to hatch. Each person has their own way to hatch eggs. There are many right methods.

If this makes you nervous, simply practice on dry grits, rice, or other tiny objects until you are comfortable with the process.


* See photo below to know what to look for on the label to tell the percentage of sodium hypochlorite in the bottle.

bleach label 8

**Pouring eggs into the solution takes time because many of the eggs or bits of leaves will stick to the container. You’ll need to move those that stick to the solution and that normally takes five to 20 seconds. At that point, you choose to either leave the original ones in longer than 60 seconds or allow the late ones to be removed early. In too long, the eggs will liquefy. In too short, pathogens won’t be killed.)

***At 60 seconds, remove the eggs IMMEDIATELY from the bleach and place them in plain water. They aren’t as fragile as you think. Moving fast is much safer than allowing eggs to remain in disinfectant longer than 60 seconds. If you move slow and careful, some eggs may be in the solution too long and become damaged. If you watch the video, you can see how this is easily done quickly, without harming any of the eggs.