Green vomit, diarrhea, and writhing caterpillars

Green liquid from your caterpillars? Maybe also writhing in the cage? We can be killing our caterpillars and not even be aware that we are doing so. Here are some questions to ask yourself if you see either of those symptoms. (Skip to the bottom to see what you can do if you find your caterpillars in this situation.)

1. Do my pets have Flea/tick medications on or in them? These medications, even weeks later, will transfer from treated pets when petted, onto a person’s hands. Medications like Frontline will be in the oils of a pet, oozing onto the pets skin. If hands are not washed and person touches caterpillar, food, or rearing container, poisons are transferred to caterpillars.


2. Do I use ANY pesticides in my house? Air conditioner ducts can carry pesticides from room to room and floor to floor. Even with sealed doors and rooms, pesticides WILL find a way to travel. The laws of science and physics seem to have lost their ability to work in these situations. Even when we think we have done EVERYTHING possible, death occurs.

3. Does my neighbor treat his/her lawn or garden with pesticides? A good rain or irrigation system can wash those pesticides over his lawn garden into and over my lawn/garden, over the roots of my plants, giving my plants the opportunity to draw the pesticides up into their systems. If he is praying pesticides, a light puff of wind can blow those pesticides into your yard. Systemic pesticides can stay in a plant for eight weeks or more. You cannot make the plant safe. If a neighbor is using pesticides, be kind. Rudeness and anger will guarantee that your neighbor will continue to use pesticides. Your only hope is to be kind.

4. Has your house been recently treated for bugs? In the south, people often have their houses treated for roaches, termites, or other pests. These treatments may cause issues for your caterpillars.

5. Did your fertilizer contain pesticides? Some fertilizers contain pesticides under other names. Try purchasing the very basic fertilizers, without bells and whistles. We personally use basic 8-8-8 fertilizer on our milkweed, no additives. It is not organic. If you wish to use only organic fertilizer, use fertilizers that are made of ONLY basic nitrogen, phosphorus, and potassium. Those are the three basic fertilizer ingredients and are not harmful to caterpillars.

6. Did you use insecticidal soap? It is often used to kill aphids and other plant pests. Because soap is not considered a pesticide, or at best is considered a safe pesticide, people don’t think of it as dangerous. Soap is not a good diet for man or beast. Just as you wouldn’t want to feed a soap covered leaf of lettuce to your child, don’t feed a soap covered leaf of milkweed to your caterpillar. RINSE WELL SEVERAL TIMES if you spray milkweed with insecticidal soap. Some insecticidal soaps will cause deformed chrysalises and/or death even if milkweed is rinsed well.

7. Did you use mosquito or tick repellent? Although many won’t affect caterpillars, some will. Again, spray or use repellents outdoors and wash WELL before touching your caterpillars, their food, or their cages.


Don’t automatically believe it. Just because the internet says it is safe, it doesn’t mean it is safe. The internet and many books have incorrect information. Check and double-check if something seems even a little odd. Yes, even check behind us. 😉 If we are offended that you check behind us, then we have a problem with our ego. That is much better than you having a problem with dying caterpillars because we were mistaken about something. If our ego gets bruised, they needed taking down a notch anyway. The caterpillars didn’t need to die.


Did you use ‘organic’ grown plants? If so, be aware that Bt is ‘certified organic’ (a natural soil dwelling bacteria) and although it does not cause green vomit and takes three days to kill, it is deadly. After a caterpillar takes the first bite, it is living dead. It cannot live. It will act as if it is hungry. Most people do not realize that it isn’t eating. Three days after it has taken its first bite of the treated plant, it will die.


Every now and then you can save your caterpillars if you catch the problem in time.

1. Immediately remove them from the rearing container and rinse them well under running water. Yes, turn on the faucet and hold them under water for a minute. For another minute or two, move them under and out of the water repeatedly, rinsing them again and again. You’re rinsing off as much of the pesticide from their skin/cuticle surface as possible. Wash your hands well with soapy water.

2. Place them on a paper towel and gently pat them dry. This will hopefully push any bits of water/pesticide that may be in the spiracles out of the opening. How effective this will be depends upon how much of the pesticide was on their cuticle and was drawn into their system.

3. Prepare a clean rearing container and place them in it. Remove the old container from the room.

4. Add fresh food (not exposed to pesticide) to the container.

Quite often caterpillars will survive if they are caught in time!