What can go wrong in a Monach-friendly garden.

Planting a Monarch-friendly garden and caring for it can be easy and fun initially, yet some issues might arise over time and can offer some challenges.

I started growing Butterfly milkweed (Asclepias tuberosa) from 2006 and Swamp milkweed (Asclepias incarnata) from 2008. The goal was to attract Monarch butterflies, but it is only in July 2018 that I finally had caterpillars on the milkweed plants. I took some inside to raise and observe them, making notes and taking photos/videos along the way (hence this website).

Monarch eggs on Swamp milkweed - © Denise Motard
Monarch eggs on Swamp milkweed
Monarch caterpillar eating its egg case - © Denise Motard
Monarch caterpillar eating its
egg case
Monarch caterpillars on Butterfly milkweed - © Denise Motard
Monarch caterpillars on
Butterfly milkweed
In 2019, I was lucky enough to be in the garden on June 17 when a female Monarch fluttered around the milkweeds and laid its eggs. The weather had been nice so far, but it turned cold and rainy for several days afterwards. This change slowed the hatching of the Monarch eggs, and some of my plants (Shasta daisies for example) started showing signs of fungal infection they never had before.

My grapes, lilacs and peonies had been infected with powdery mildew the year before. As a preventative measure in 2019 I sprayed an organic homemade mix of garden sulphur with a strong tea of roman chamomile and oregano on the affected plants, both at the end of May and June.

I had checked the properties of these products prior to spraying and they were all supposed to be fungicides, but NOT insecticides. I was careful to spray at the end of the day when the wind was calm to prevent spray drifting.

Then finally the Monarch eggs started hatching and the baby caterpillars could be seen munching their way through Milkweed leaves and flower buds (see this page for photos and videos of them). That is, until around July 7. I had been checking on them at least once a day, then almost overnight they vanished. All over the garden. It was baffling.

Something happened to them, but what? Then I found a black spot on a Milkweed leaf that looked like a dead caterpillar. I took it to Dr. Christine Noronha, entomologist and research scientist for Agriculture and Agri-Food Canada in Charlottetown, PEI. I asked her if that caterpillar could have died of a fungal disease, due to the cold and wet weather we had.

Dr. Noronha said it was a caterpillar molt and that it did not show any signs of fungal disease. Shortly after I did find one small live caterpillar, which I took inside to 'save' it from I-did-not-even-know-what in that garden. I called it the 'Last One Alive', and it turned into a healthy female butterfly.

2nd and 5th instar Monarch caterpillars on Swamp milkweed - © Denise Motard
2nd and 5th instar Monarch
caterpillars on Swamp milkweed
Swamp milkweed flowers - © Denise Motard
Swamp milkweed flowers
Monarch chrysalis under Lilac leaf - © Denise Motard
Monarch chrysalis under Lilac leaf
What added to the mystery is the fact that I had given about 30 Swamp milkweed plants from my garden to the Stratford Watershed Group to help them start their own Monarch butterfly garden. There were eggs on those plants, and when I went to check on them over the following weeks, the caterpillars in their garden all grew healthy and plump.

So why did mine disappear, and those I gave away were OK? Yet they started in the same garden, and probably had the same female butterfly 'mother'. What was different in my garden from their garden? Two things actually.

The first one is the fungicide I used. After checking again I found more sources of information mentioning insecticidal properties for the three products I combined - garden sulphur, chamomile and oregano tea. I even found out that oregano oil is used as an insecticide in grain and cereal warehouses, for example.

Then I realized that most of the plants I had sprayed were very close to Milkweed plants, and it was highly likely that some spray would have drifted on the Milkweed, even with the best of precautions. Guilt started to sink in - I'm supposed to provide Monarchs with a friendly environment, not kill them!

There was also another possibility I considered, due to the fact that I never found any dead caterpillar on or around the plants (although those caterpillars were so small that once on the ground they would likely not have been found anyway). They might have been eaten by some predator in my garden, but that was absent in the Stratford Watershed Group garden. But which one?

The potential predator I know their garden doesn't have and that I DO have is the Ruby-throated Hummingbird. They don't have any (yet) due to the location of their new garden (in the middle of a large lawn). Hummingbirds feed on nectar (natural and artificial), but they also prey on insects and feed their chicks with them.

Female Monarch butterfly on Swamp milkweed flowers - © Denise Motard
Female Monarch butterfly on
Swamp milkweed flowers
Swamp milkweed clump - © Denise Motard
Swamp milkweed clump
Fresh Monarch chrysalis twisting and pushing to secure cremaster hook into silk pad - © Denise Motard
Fresh Monarch chrysalis twisting
and pushing to secure cremaster
hook into silk pad
Large Monarch caterpillars are full of cardiac glycosides, a toxic substance from Milkweed that they accumulate in their bodies, which provides them with a good protection from predators. But the eggs and small caterpillars don't yet have that defense. If a hummingbird has 'decided' to hunt for them, those eggs and baby caterpillars would have disappeared without a trace in no time.

The irony here is that I have grown hummingbird-friendly plants also from 2006, in addition to providing them with a nectar feeder before the plants would bloom. These birds have always been around, my garden is now their 'territory'. Is their presence compatible with that of Monarch eggs and tiny caterpillars?

And why did I have all those Monarch caterpillars the year before, while the hummingbirds were also all around the garden? Could it be that in 2019 one of those birds 'tried' some Monarch eggs and baby caterpillars by chance, and found them tasty?

Something else also happened that summer. I did see Monarch butterflies several times in the garden, and some were females based on their behavior stopping on Milkweed leaves. Sure enough I did find more eggs following their visit, but most of those eggs were vanishing without a trace after a few days.

For the rest of the summer I kept checking the milkweed plants in search of small caterpillars, and I was able to find just a tiny few. Those numbers were much lower than what should have been expected from the number of eggs I saw, and also from all those butterfly visits I was able to witness. It seemed like there was a ongoing threat.

Ripe Milkweed seedpods - © Denise Motard
Ripe Milkweed seedpods
Monarch caterpillar in 'J' phase, soon to turn into a chrysalis - © Denise Motard
Monarch caterpillar in 'J'
phase, soon to turn
into a chrysalis
Tagged Monarch butterfly - © Denise Motard
Tagged Monarch butterfly

Here is a list of steps I have taken to improve the environment for Monarch eggs and tiny caterpillars in my garden, given the circumstances. 

The Butterfly milkweed plants have a low level of toxic cardenolides, as compared with Swamp milkweed for example. It is this toxin which makes the Monarch caterpillar unattractive to predators, so the more they ingest the better. So I uprooted all those plants at the end of October, after all the Monarchs were gone.

The advantage of Swamp milkweed on Prince Edward Island is also that it is a native plant. It would not be recommended to plant Common milkweed in this province because it is invasive due to its system of rhizomes (and is not a native plant).
The ruby-throated hummingbird  is well established in the area and already has plenty of flowers to feed from, even at the beginning of the season. Fish and wildlife agencies do not recommend feeding wild animals, and this should include wild birds.

When birds get their food from artificial sources, such as syrup feeders for hummingbirds, they are feeding less from their natural sources of food. In the case of hummingbirds, this means that they are not pollinating flowers as much. Pollination is one important role these birds have in Nature.

Since hummingbirds are more attracted to colorful flowers, such as red, orange and pink ones, I also got rid of all my pink Swamp milkweed and only kept the rarer white variety. The goal is to make the blooming milkweed less attractive to these birds.

Just keeping white swamp milkweed will not deter the Monarch butterflies from laying their eggs on those plants, as I have already found several eggs and young caterpillars on the white plants I have. 

NO MORE SPRAYING DURING THE MONARCH SEASON It goes without saying that there will be NO MORE spraying of any homemade organic pesticides (the only ones I use) during the Monarch season. This means from the beginning of June to the end of October, just to be sure.

Ants have a very powerful sense of smell. They are able to detect the fragrance of nectar-rich flowers (such as milkweed) from several meters away. If there are Monarch eggs or tiny caterpillars where they look for nectar, they would likely prey on them. A study has found that up to 69% of predatory arthropods on Milkweed were ants.

One yet-to-be-tried deterrent to keeping ants off the Milkweed plants would be to place something at the base of the plants that would confuse their sense of smell and prevent them from crawling up the stems. Since Swamp milkweed grows in clumps this should be feasible. This 'something' should not be damaging to Monarch caterpillars when they crawl down milkweed stems in search of a spot to pupate.

Wasps are attracted to nectar-rich flowers, and being predators they will also likely take Monarch eggs and baby caterpillars if they find some.

To deter wasps from visiting the blooming Swamp milkweed for nectar, installing a fake wasp nest visibly on a structure near the plants should do the trick. These insects are territorial and if they see a nest already in the area, they should stay away.

All those measures are currently based on assumptions about what might have happened in the garden. Hopefully some of these assumptions will be validated in the summer.


SPIDERS - Any healthy garden has - and MUST have - spiders, and mine is no exception. There are spiders on my Milkweed, but I leave them alone because they are helpful arthropods. However they DO prey on Monarch eggs and young caterpillars. This is a predator against which there is not much to be done unfortunately.

EARWIGS - These arthropods also prey on Monarch eggs and larvae, and are active at night. During the day they rest on plants in crevices of young leaves or flower buds. These areas are the same ones where Monarch eggs and young caterpillars would be found. Any solutions?

Even LADYBUGS, which are very helpful pest-eating insects, will also prey on Monarch eggs and young caterpillars.