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.

Remember:

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.

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.

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.

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.

Does that mean the plant is safe for caterpillars? Absolutely not.

People are excited when nurseries stop using neonicotinoid pesticides. Of course! It’s a good thing. The question is whether we remember that neonicotinoids are only ONE grouping of pesticides. There are many pesticides that are not neonicotinoids.

Two plants can be grown exactly the same, next to each other, one treated with neonicotinoids and the other with a non-neonicotinoid pesticide. Caterpillars eating either plant will be just as dead.

Remember, the fact that a plant isn’t treated with neonicotinoids doesn’t mean it is safe for caterpillars.

When the mosquito fogging/spraying truck comes down your road or your neighbor sprays in his yard, what does that mean for your butterfly/pollinator garden? It can mean disaster. Or it may not affect your host plants at all.

Part of what determines the effect it has on your plants depends on several factors.

1. Type of pesticide: what are the active ingredients?
2. Is it a systemic or non-systemic pesticide?
3. Where are your host plants located?

1. Pesticides cause different symptoms in caterpillars, depending on the active ingredient. Whether it is organic or not doesn’t make a difference. Organic pesticides are as deadly as inorganic pesticides. What matters is the mode of action of the ingredient. Does it affect the nervous system, growth changes, or something else? As homeowners, we have no voice in the pesticide that is used. So, even if we know how it would affect our caterpillars, that bit of knowledge can’t actually help us at all.
2. Is the pesticide non-systemic (lasts only a few days) or systemic (lasts for months)? If it is non-systemic, covering our plants before the fogging/spraying happens can help if we wait a good 9 hours before removing the covering. If it is systemic, it can be washed into the soil and the plant draw it up into its system. If systemic pesticides are used near you, growing host plants in pots placed on saucers can help. This prevents water from reaching the roots as it flows across your yard.
3. Where are your host plants located? This is the area where you have greatest control. If your host plants are close to the road, where a fogging truck passes, you will see more deaths after the county fogs for mosquitoes. If your host plants are close to your neighbor’s yard, it would be easy for over-spray or wash to reach your plants. By planting your host plants away from the road and your neighbor’s property, you gain a great deal of control. Over-spray won’t reach very far except on windy days. Rain or irrigation water can wash the spray over into your lawn. Planting uphill from your neighbor, if possible, offers additional protection.

As we talk about pesticides, I want to again mention that those of us who must have our houses treated for termites, we should either plant at least 15′ away from the house foundation or plan treatments at the end of the growing season, about the time of your first hard freeze. For some of the US, this means that the systemic pesticide has time to work out of the plants before the last freeze and plants are growing again. (For the northern states, pesticide may take longer to work out of the soil. It is possible that termite treatment is not available just before the first hard freeze. If it is not, planting host plants away from the foundation may be your only option.)

There are some cities and counties that have caring people in the right job. A nice, polite, and short letter or visit may do a great deal of good. Some counties will avoid spraying in front of a house where someone has asked for their property not to be treated. Rudeness and anger rarely bring the desired results, so politeness and education is the key.

Remember, if your caterpillars have been exposed to pesticide, you can try saving them. This does not work with all pesticides, only a few.

One of the wonder advantages of living in a city or subdivision is that there are neighbors to help when we need help. One of the disadvantages is that if they are too close, many things that they do will affect us.

Although it was believed for years that Monarch butterflies in the eastern US and the western US were genetically different, DNA studies have proven that they are the same.

There are two groups simply because they do not naturally fly over the Rocky Mountain Range as they migrate and fly about to mate and lay eggs. The western Monarch butterflies usually stay west and the eastern Monarchs usually stay east. Although Monarch butterflies have been seen in the Rocky Mountains, in high altitudes, it is not their natural flight direction. Unless they are migrating, they seek out milkweed and nectar plants, males searching for female butterflies which are often around milkweed and nectar plants.

The practice of tagging and releasing Monarch butterflies has revealed a fact that was not expected. First, some western Monarchs will migrate to Mexico. They are tagged in the west, wild Monarchs, and the tags are found in Mexico.

Second, it was discovered that if a Monarch raised west of the Rocky Mountains is moved to the Eastern US and released, it will migrate to Mexico and vice versa.

Migration destination depends on where it is located when it begins migration, not where it was when it emerged as an adult butterfly. Its DNA signals it what to do depending on its location at the current time and which direction to fly, depending on where it is when it is captured, tagged, and re-released.

This map is a Monarch Watch map, the information based on recovery of tagged Monarch butterflies.

Dr. Tom Emmel, University of Florida, believed that some Monarchs fly down Florida to Cuba to stay in mountains there. Some, after arriving in Cuba, he believed would fly to the Yucatan Peninsula and over to the overwintering sites in Mexico.

Although the genetics are the same in both eastern and western Monarch butterflies, the USDA does not permit them to be shipped across the continental divide.

Mia Munson provided this link to a Monarch Watch webpage that mentions the DNA study.

Quite often people will ask why a caterpillar that is known for hosting on one plant is eating a different one. Even today, people are discovering new host plants for species. Some eat it only in captivity and others eat it in the wild. But the question we first must ask is, “IS it eating the plant?” Quite often, it isn’t eating it at all.

Caterpillars move off a host plant for several reasons. Some move off to molt, to pupate, or simply are lost, working their way back to their host plant.

We’ve seen many species of caterpillars on plants that weren’t their host plants. Almost every time, they were molting or pupating.

Much to our amazement, we found a Buckeye chrysalis on a snail. You never know where they will choose to pupate.

We had Buckeye butterflies in a screened garden room. To my surprise, they stripped a butterfly bush (Buddleia davidii) of leaves, pupated, and emerged with no problem. Later we found caterpillars on butterfly bush in the wild. Evidently it happens but rarely.

Although there was no question whether the Buckeye caterpillars were eating butterfly bush leaves, we did tests, feeding that particular bush to caterpillars in captivity. They ate it with no problem. We tried another butterfly bush, one that bloomed a different color, and they all died. We bought the lavender blooming bush from a nursery without a label. When we returned to the nursery, they had no idea which cultivar it was.

Monarch butterflies often pupate on milkweed. They also often pupate off milkweed.

Sometimes a caterpillar eats eggs, another caterpillar, a pre-pupa, or a chrysalis, even when there is enough food. Why?

When we stop to think about it, we realize that an caterpillar is simply a mature egg plus host plant. A pre-pupa is addition of time and more host plant. A chrysalis is the addition of … you get the idea.

Because a caterpillar, pre-pupa, and chrysalis are made entirely of the host plant, so to speak, the taste of the insect would be tasty to caterpillars that eat the same host plant, whether they are the same species or not. We know that some caterpillars that eat distasteful plants are distasteful to many predators. The taste of the host plant controls the taste of the insect.

The instinct of some species of caterpillars, when they hatch, is to eat its egg shell. Once that shell is eaten, if there is another egg nearby, that instinct may cause it to continue eating eggs.

Although it happens more often when caterpillars are contained and run out of food, cannibalism happens even when there is plenty of food available.

Cloudless sulphur caterpillars are well known for cannibalism, out in nature. Even on a large host plant, they often attack and eat other caterpillars. They are one species that are often raised separately, one per plant stem.

Pipevine swallowtails and gold rim (polydamas) swallowtails are extremely cannibalistic in captivity. Once they are near pupation, many farmers raise them separately. As young caterpillars, they are gregarious, staying together on a leaf. Once they grow to three or four instars, they naturally separate on the plant.

To be safe, simply make sure they have plenty of food and learn which species tend to cannibalize in captivity. Separate them at the appropriate age.