Plants and pesticides – how long to wait?

Enthusiasts often run out of leaves for caterpillars and rush to the nursery to buy more plants. Then comes the BIG question: How long should I test it with one caterpillar before placing more caterpillars/leaves together? You won’t like the answer.

Pre-pupae were unable to pupate properly, due to insecticides.

First, to be 100% sure, until it becomes an adult and flies away without problem. If a caterpillar is exposed just before pupating, some insecticides won’t affect them until they emerge as adults. If some pupae are exposed, it won’t affect them until they emerge as adults. The adults will expand and dry their wings, but when they start to fly around, they go into spasms, usually eventually dying with their wings folded over their legs.

Next, at least into chrysalises. Some insecticides (such as used in some oral flea/tick medications) will affect them only when they begin to pupate. The result is deformed or incomplete chrysalises.

Caterpillar dying from insecticide.

If you don’t have that much time and MUST feed the leaves to your caterpillars, wait three days if at all possible. The certified organic pesticide, Bt (a natural soil-dwelling bacteria), takes three days to do it’s job. Three days after caterpillars eat it, the caterpillars die.

Many insecticides will cause almost immediate vomiting (green fluid that stays green) and sometimes convulsions. This isn’t a pain reaction. It’s a nerve reaction. The insecticide acts on certain nerves, causing the caterpillars to jerk around.

Greenish stains are from spitting. They stay green or yellow.
Black/gray stains are from dried hemolymph. Within five minutes of hemolymph (like blood) being exposed to air, it turns black/dark.

Bottom line – the longer the better, up to the adult emerging and flying away.

Pipevine Swallowtail vs Polydamas Swallowtail?

For folks who live in Florida, Southern Texas, and below Tuscon, Arizona, your pipevine plants may be visited by two different swallowtail butterflies. This can cause a problem because most plants that Pipevine Swallowtail caterpillars can safely eat will kill Polydamas Swallowtail caterpillars and vice versa.

Now it’s a bit easier for you. Click here to visit our page that shows the difference in egg, larva, chrysalis, and adult forms of these two species.

Can you tell which is Pipevine Swallowtail and which is Polydamas Swallowtail?

Southeastern U.S. Butterflies and Their Plants

Butterfly species vary from area to area, state to state, and region to region. Plants chosen for a butterfly garden in Florida many not be the best plants for a garden in New York or Oregon.

For the Southeastern US, these are some of the plants that would be great in a butterfly garden.

  • Pawpaw for Zebra Swallowtail
  • Pipevine for Pipevine Swallowtail
  • Fennel, parsley, dill for Eastern Black Swallowtail
  • Black cherry, tulip poplar for Eastern Tiger Swallowtail
  • Spicebush, red bay, sassafrass, for Spicebush Swallowtail and Palamedes Swallowtail
  • Milkweed for Monarch and Queen
  • False nettle, hackberry, for Eastern Comma, Question Mark, Red Admiral
  • Passion vine for Gulf Fritillary, Zebra Longwing, Variegated Fritillary, Julia
  • Asters for Pearl Crescent
  • Willow, hackberry for Mourning Cloak
  • Willow, black cherry for Red-spotted Purple
  • Willow for Viceroy
  • Hackberry for Tawny Emperor and Hackberry Emperor
  • Hackberry for American Snout
  • Senna for Cloudless Sulphur, Orange-barred Sulphur, and Sleepy Orange

Many of these plants are available online from Shady Oak Butterfly Farm.

Should I or should I not? What do you think?

There is a concern expressed by enthusiasts who want to remove the head capsule from a molting/molted caterpillar. Should you? Or not?

A Monarch caterpillar with its old head capsule over its mouth, molting.

There are two beliefs on this. One belief is that, if it molted and can’t get its head capsule off, an enthusiast should remove it to allow it to eat and grow. The other belief is that, if it didn’t take it off naturally, removing it and allowing it to live and lay mate may pass on a defective gene, one that may have interfered with the molting process.

A Monarch caterpillar in the process of actively molting.

There is a challenge to be sure that it has finished molting. Removing it too soon will kill it. If it has been observed molting and it has been a while with the head capsule still on its mouth, what do you think?

What are your thoughts? Please comment below.

Spit/vomit or blood?

Green liquid with caterpillars normally means either stress or insecticides. Some species immediately spit when they are touched. Skippers are notorious for this reflex. Other species tend to spit when they have been exposed to insecticides. Because of this, green stains in with caterpillars is a sign of possible problems.

But their hemolymph (comparable to blood) is also green. When we see green, how do we know if it is hemolymph or spit? Simple. Spit stays green and hemolymph turns dark within five minutes.

A crushed chrysalis has spilled out green hemolymph (their version of blood). Within five minutes, hemolymph turns dark or black. Spit/vomit, from insecticide exposure, stays green.
A Monarch caterpillar walked over a fresh chrysalis, tearing its cuticle (like skin), and leaving a trail of footprints in hemolymph.
Watch for green, like in this photo. When you see it, check for insecticide exposure. Remember, flea/tick medication is also an insecticide.

Remember, oral and topical flea/tick medication is also an insecticide. The ‘medication’ (insecticide) is exuded by your dog’s body through his skin and dander. When you pet your cat or dog, you are transferring the insecticide from your dog’s body to your hands.

Use of insect spray/treatment even in rooms behind closed doors on the other end of the house can travel through the air and a/c ducts to the room where caterpillars are eating. A spray was used 30′ away from this habitat with closed doors between the habitat and the spray. Every caterpillar died.

All the caterpillars in this habitat died from an insecticide used 30′ away behind closed doors.

What color is the Monarch chrysalis shell?

When we see a green Monarch chrysalis, we think of it as a green shell/cuticle. Actually, it’s a pale green. The bright green we see is the developing butterfly.

Maturing Monarch chrysalis/butterfly

As the butterfly matures, we see the color begin to form a day or two before it emerges.

We took a badly deformed chrysalis and euthanized it. We scraped the contents off the shell. This is what the shell looks like without a developing butterfly inside.

An empty Monarch chrysalis is pale green, not the rich green that we associate with Monarch chrysalises.

Protect the plant!

It’s delightful when caterpillars eat the plants enthusiasts grow for them. We watch them grow, pupate, and emerge as beautiful adults. We release them into our yards and other areas. BUT …

… before long, while using the same plants once they grow new leaves, there are caterpillar disease issues. We didn’t treat the plant with insecticides. We can’t figure out why they are dying.

Diseased Gulf Fritillary butterfly caterpillar

If we have used living plants and reuse the same plants, what about the disease pathogens they may leave on the plant, pot, and soil? Some butterfly diseases are so slight that they aren’t noticed at first. After a while, the pathogens build up and young caterpillars, the next generation or two, eat the pathogens after the plant has grown new leaves.

If only there was a way to protect the pot and soil! Oh, wait … there IS!

Simply take a plastic bag and cover the pot. This is a great use for plastic grocery bags. Tie it tight around the stem.

Protect the pot and soil from disease pathogens by tying a plastic bag around the pot and over the soil. Plastic grocery bags are perfect for this purpose.

Once caterpillars have eaten the leaves, cut off the bag and dispose of it. Cut the plant back to only a few inches tall. In a few weeks, it will bush out and be ready for more caterpillars.

A tropical milkweed plant branches beautifully once it has been cut back to 3″ tall.

If you water the plant well before tying the bag shut, you won’t need to water it again until you take it out of the popup habitat. The plastic bag usually keeps the soil moist for a week or more.

Polydamas or Pipevine?

Finding eggs on pipevine plants is exciting. For most of the United States, it is easy to know which laid the eggs, Polydamas (Gold Rim) Swallowtail or Pipevine Swallowtail. For the states where both species are found, confusion can reign.

Gold Rim (Polydamas) Swallowtail and Pipevine Swallowtail eggs
were laid on the same pipevine plant.

It is simple to tell the difference. Pipevine Swallowtail eggs are burgundy red. Polydamas (Gold Rim) eggs are yellow.

Top: Pipevine Swallowtail burgundy-red eggs
Bottom: Polydamas (Gold Rim) Swallowtail yellow eggs

Although female butterflies usually lay eggs on the correct species of pipevine, sometimes they make mistakes. Here is a partial list of which pipevine species are a host for which butterfly species.

Mosquito spraying … what to do?

Mosquito spraying can kill caterpillars. In Florida, the government has been testing different sprays for a few years, adapting to find the insecticide that is most damaging to mosquitoes and least damaging to butterflies. We’ve supplied the caterpillars and adults for these tests for nearly ten years. I wish all states would do the same, test the insecticides on local native species of butterflies. It is better to sacrifice some with the goal of saving a larger number in the short and long run.

If you know the fogging truck is coming or they will be doing aerial spraying, cover your plants quickly.

Approach your city/county agency that is responsible for fogging/spraying with trucks. Explain the situation with Monarch butterflies. Be prepared with government articles/documents printed out and take them with you. Read the articles first and make sure you understand them so you can discuss the situation yourself. You can find some government articles online. Ask them which insecticide is being used. Do research and find out how the active ingredient works. Does it affect only mosquitoes? Does it affect caterpillars and butterflies? Ask for your area (in front of your house) not be sprayed.

To talk to someone about aerial spraying, talk to the people who make those decisions on the state level. Again, be prepared with good, reliable, accurate information. Ask that you be notified before they spray. Because of drift issues from air spraying, asking not to be sprayed may do little to zero good. They may do their best to avoid your yard but a simple gust of wind can change all that. Prior notification is safest.


1. Be prepared with articles from reliable sources, preferably a government agency or university publication. Understand the articles yourself so you can discuss them intelligently.

2. Don’t be afraid to say, “I don’t know but I’ll research and find out.” Saying something as fact that is inaccurate will undermine all your efforts. If they know you’re not telling the truth about something, why should they believe anything you say?

3. Be kind. Be patient. Don’t be angry. Use a calm tone of voice. Anger, yelling, name-calling … all these undermine your efforts. Few people will respond well to threats or anger. Most will decide, right then and there, that they don’t want to reward rudeness and bad behavior by doing what you want. One person, recently, made a difference by staying calm and being kind. When the decision was made to do what she asked, she was told that the reason it went her way was due to her attitude more than anything else. Remember, the person you are talking with is rarely the one making the decision. You need that person to move your request to a higher level, or to tell you who to talk with about the issue who has the authority to make those decisions. Don’t blame the person who is simply doing his/her job and cannot, by any stretch of the imagination, make those decisions.

4. In some areas, the decision to spray is about human lives. In south Florida, there were some bad mosquito-borne diseases around in the last decade. Those involved in spraying need to know that you value human lives too, more than butterflies. We may disagree on how to protect human lives but when you argue against spraying altogether, it will be translated as valuing butterflies more than humans. Sometimes it isn’t the truth that matters (that you do value humans more) but the perception that the other person has. (The official who can’t imagine any other way to control mosquitoes will think you value butterflies more than humans if you attack any and all mosquito spraying.)

Side note: Be aware that the insecticide can become active in water and run over and splash onto your plants. If your plants are in pots, don’t place the pots directly on the grass or soil. Place them in saucers or on bricks/rocks, lifted off the ground. Keep your sheets or whatever you use to cover your plants in a readily accessible area so you can grab and cover in just a few minutes. When you hear that truck, you may only have two minutes.

Don’t plant host plants next to my house? Why not?

It’s our instinct to plant beautiful host plants next to our house. In reality, it is best to plant them 20′ and more away from the foundation. If your house is on a slope, plant host plants uphill, not downhill.

Aquatic milkweed – Asclepias perennis

Too often people end up with an insect that is causing problems, such as termites, roaches, or ants. When the house and/or foundation is treated, the insecticide can travel laterally though the soil 15′ and more. The insecticide will then be absorbed by the host plant’s roots and the plant will become deadly to our caterpillars.

If we plant downhill, a good rain or irrigation will wash the insecticide down the slope to the roots of host plants, causing them to become deadly to caterpillars.

A Queen caterpillars eats a leaf of Charlotte’s Blush variegated milkweed

When we had termites in our walls, we caught it in time. Our foundation now must be treated every year but our house did not need to be tented. Each time, ant beds within 15′ of the house are soon covered with a thick layer of dead ants. Two months after treatment, I mistakenly used cudweed growing next to the house to feed American Lady caterpillars. Every one died.

Because we live in north Florida with sandy soil, we are able to have our house treated in late fall, after butterflies quit laying eggs. By spring, when butterflies begin laying eggs again, the insecticide is washed away. In the north or where soil has a good deal of clay or loam, this may not be an option. We no longer plant host plants near our house, even though we changed treatment time to late fall. It just isn’t safe enough for butterflies.