Project Swallowtail Plant List - Key plants for Swallowtail Butterflies

This is the first of several pages that will list native plants we are using to support native pollinators in Project Swallowtail. This page highlights species we're using to support native Swallowtail butterflies. Other pages will give more complete list of trees, shrubs, perennials, and grasses beneficial to different birds, bees, butterflies and other pollinators.

But first, let me direct you to a previous post on just this subject: Hops and Spice, Pipes and Paws - How Large a Tale will you Swallow? That post has fun with some of the history around these plants, animals, and human customs.

Our plant list for swallowtails:

• Hoptree
• Pipevine
• Pawpaw
• Spicebush
• Sweet crabapple
• Tuliptree
• Black cherry
• Pussy willow
• Aniseroot
• Golden Alexanders
• Great Angelica
• Anise, caraway, coriander, dill, fennel, lovage, and parsley

Details - see below!

Giant Swallowtail

Giant Swallowtail, Gordon Roberton CCbySA3.0

There are only two Ontario native plants Giant Swallowtail caterpillars will eat, and one of them, Prickly Ash, is a monster in the garden. Don't go there, unless you have a big property, and you want to be able to say, as Sean James does, "kiss my Prickly Ash" to annoying visitors.

Instead, we're planting Hoptree (Ptelea trifoliata). This shrub to short tree (up to 6m tall but can be pruned much shorter; 2-3 m along the shores of Lake Erie) thrives in the sandy soils found in our area, and is not too particular about light or moisture. 

Ptelea trifoliata 'Aurea' ; photo Karl Gercen

We'll be using plants grown from local seed, but if you are into foliage colors you can consider the variety "Aurea" which won a RHS Award of Garden Merit for its pale spring leaves.

I wrote about hoptrees and giants in this post which you can peek at for more details, including how to grow your own from seed.

Be sure to look online for images of Giant Swallowtail caterpillars so you can recognize them when a female has found your bush! 

Pipevine swallowtail, ©Troy Bartlett

Pipevine Swallowtail

Here's another butterfly with only a single native host, the pipevine Aristolochia macrophylla. This Appalachian species is at the northern limit of its natural range with us, although it was in much demand a century ago as a way of shading porches. The pipevines are a large family in the tropics, and they all share compounds in their leaves which are very bitter if eaten. Like the monarch does with milkweed, Pipevine swallowtail caterpillars store up these bitter compounds so that the adults are very nasty tasting for birds.

Pipevine can be a vigorous grower where it is happy. A fence is an ideal spot for it, like the big spread of it on Ward's Island near the Island Cafe, which used to harbour many of these butterflies. Most soils are OK, but the vine doesn't like to be too dry. I've seen it growing well in half shade.

Zebra Swallowtail

The only local host for the elegant Zebra swallowtail is the pawpaw tree, whose very tasty fruit is a fine
reward for pollinator gardeners in the fall.

It takes two different pawpaws to cross-pollinate and set fruit, and being a small tree they may take five years after planting to reach blooming size. But after just a few years zebra swallowtails can lay eggs on the leaves - they don't care about the fruit.

In nature, pawpaws are often found in moist soil near streams or rivers, and can tolerate partial shade. Once they reach blooming size, they send up new stalks from suckers. I trim mine off once a year, a 10 minute task.

My two pawpaws were grown from pawpaw fruit from the Niagara area, sold by a farmer in the Dufferin Grove Organic Market. I know of at least two other properties in our area with large, well-yielding pawpaws.

Spicebush Swallowtail

Spicebush swallowtail

Compare the blue hind wings of the Spicebush and Pipevine swallowtails. They are part of what biologists call a mimicry complex. Lindera benzoin - Spicebush - is the favored host plant for Spicebush caterpillars, and also for the Promethea moth. The Tiger Swallowtail and the Imperial moth also feed on the leaves.

Spicebush has small but fragrant yellowish flowers in spring and red fruit in fall, although there are separate male and female plants, so you need one of each within a few back yards of each other to get fruit. Fruit, leaves, and stems are aromatic and have been used in teas and other recipes.

Spicebush blooms more in the sun but tolerates shade very well. My bush is planted north of an old pear tree where it gets several hours of afternoon sun.

These swallowtail caterpillars can also feed on Tuliptree leaves - see the Tiger Swallowtail, below.

Male spicebush flowers - public domain

Imperial Moth, Joel Mills, CCbySA 3.0

Tiger Swallowtail

Eastern Tiger Swallowtail, Derek Ramsey CC by SA 3.0

As a child I didn't know that "Tigers" could be one of several very closely related species. The USA tiger's caterpillars feed on Tulip Trees and a fair number of other trees, the Canadian tiger replaces tuliptrees with poplars, and there is a hybrid species left over from the ice ages in the Appalachian mountains. 

To add more to the confusion, the females can either be traditionally tiger-colored or have a black form which looks a great deal like the Black Swallowtail (below).

There are about 7 or 8 host plants for the Tigers, but the ones we are featuring in Project Swallowtail have benefits for other pollinators too. These are the Tulip Tree, Black Cherry, Sweet crabapple, Pussy Willow, and our friend the Hoptree (above).

crabapple, Per Palmkvist Knudsen,
CCbySA2.5

Sweet crabapple

Malus coronaria is native to our region and an excellent small garden tree, for pollinators in spring, caterpillars in summer, and birds in fall. Full sun produces the greatest bloom and fruit set. Jam is delicious!

Tulip tree, Clement Kent CC by SA 3.0

Tulip Tree

Liriodendron tulipifera is a native giant magnolia - up to 50m/160ft in the south. An excellent shade tree, we planted it in Kathy's Garden to give shade and beauty to seven future generations, as the ash and beech and Austrian pine trees around it die over the next few years. It's valued for its wood.

Honeybees love tuliptrees in bloom, and make a flavour-rich dark honey from it. A friend gave me a jar of it from a grove in Ohio, which I save for special occasions.

Tuliptree Silkmoth, Thomas Barnes Public Domain

Tuliptrees are native to Carolinian Canada, but used to be rare in Toronto. A friend now grows them as far north as Creemore. The City of Toronto has added them to the list of trees the city will plant for free in your front yard if you ask. Several in the Dufferin Grove neighbourhood have now reached 3 stories tall - this tree can grow several feet per year when young!

 It hosts "only" 28 species of native moths, including the giant Tuliptree Silkmoth, and of course the tiger swallowtail.

Black Cherry

Prunus serotina is like sweet crabapple - flowers in spring, leaves in summer, and fruit in fall for birds. It's like tuliptree as it is a large tree with valuable lumber which can live hundreds of years. 

I had a property on the shore of Lake Huron with one enormous Black Cherry and several of its children. The big tree had been struck lightning but survived. Just down the hill to the lake grew Alternate-leaved Dogwood, whose blue or purple berries ripened just after the cherries. We had torrents of birds for those weeks!

Emperor moth. Jena-Phillippe Harmon, CCbySA 3.0

Talk about beauty: Coral Hairstreak, Eastern Tiger Swallowtail, Red-Spotted Purple, Spring Azure and Viceroy butterfly and Io, Cecropia, Promethea, and Emperor moth caterpillars feed on the leaves - it's one of the top trees in ecologist Douglas Tallamy's list of best trees for wildlife.

Pussy Willow

Pussy willow - Silk666, CCbySA 3.0

The native willow Salix discolor is a champion at supporting pollinators, and children! A few stems of "pussies" is one of the finest signs of spring. Keep them in water for a few weeks and you'll find roots on the lower stems. Plant them out in a sunny, moist spot and in just a few years you'll have pussies of your own to give away.

I watch my cut stems carefully. Pussy willows have male and female plants. If the soft white of the buds is replaced by golden pollen-bearing stamens, you have a branch from a male tree. The early spring pollen is incredibly valuable to early spring bees, including honeybees and bumblebees.

And the butterflies and moths! Another Tallamy favorite, pussy willow supports Acadian hairstreak, black-waved flannel moth, cecropia moth, Compton's tortoiseshell, cynthia moth, dreamy duskywing, eastern tiger swallowtail, elm sphinx, imperial moth, Io moth, modest sphinx, mourning cloak, polyphemus moth, promethea moth, red-spotted purple, small-eyed sphinx, twin-spotted sphinx, and viceroy. In fact, a small grove of willows is one of the best ways to guarantee seeing mourning cloak butterflies on mild days in late fall and early spring. 

OK, enough about Tigers and their hosts. One more swallowtail to go:

female black swallowtail, Kenneth Dwain Harrison CC by SA 3.0

Black Swallowtail

The black swallowtail Papilio polyxenes is probably our most common swallowtail. Males and females are both black but differ in the amount of blue (mimicking the pipevine swallowtail).

male black swallowtail, D. Gordon Robertson CC by SA 3.0

Males defend mating territories fiercely, and if you visit a hilltop in High Park in summer you may see an aerial battle between two males. 

Females search for plants from the carrot/Queen Anne's lace family to lay their eggs. Given the abundance of the invasive but well established Queen Anne's Lace (wild carrot), they don't have to look far.

If you want some native plants to feed black swallowtail caterpillars and provide blooms for other pollinators, I recommend three. 

The dappled-shade adapted Aniseroot sweet cicely (Osmorhiza longistylis) has anise-scented and flavoured leaves and springtime white flowers. 

Golden Alexanders
Derek Ramsey CCbySA 3.0

Golden Alexanders (Zizia aurea) has beautiful yellow clusters in May or June; it dies back if the soil gets dry. In addition to the black swallowtails, the solitary mining bee Andrena ziziae feeds its young only the pollen of Golden Alexanders. I have it in a spot with half a day's sun.

Great Angelica (Angelica atropurpurea) is a native perennial we should know better. Its sweet stems and roots were used for making candy, and Indigenous peoples have a number of medicinal uses for it. With golden blooms on purple stems three to six feet tall, it is a major plant in the water or rain garden. It needs moist soil and a reasonable amount of sun. Hordes of smaller pollinators will be attracted to the blooms.

Black Swallowtail caterpillar
@401rooftopgarden  - CC by SA 3.0

And then, there are all the non-native but delicious herbs that will feed black swallowtail caterpillars. Anise, caraway, coriander, dill, fennel, lovage, and parsley are some of the more common ones. On the rooftop garden of 401 Richmond in downtown Toronto, gardener Saskia Vegter found caterpillars last year, showing that apartment dwellers can attract this butterfly.

Hops and Spice, Pipes and Paws: How Large a Tale will you Swallow?

Smoking in a Tavern: David Teniers the Younger

What image comes to mind, Dear Reader, when I speak to you of hops and spice, pipes and paws? For me it is one of those archetypal Dutch Tavern scenes of perhaps four centuries ago. The pipes of the smokers, the dog on the floor (proving that taverns in old Holland and restaurants in present day France are more civilized than we overly prissy Canadians), the jugs of spiced wine or the mugs of hopped ale were essential elements of a school of Pays Bas artists such as Matthijs Wulfraet, David Teniers the Younger, and Gerrit Dou (a student of Rembrandt).

Self Portrait - Gerrit Dou

Let’s start with pipes, shall we? Although pipes had been used for smoking substances such as hashish in Asia and the Middle East, it’s fair to say they were invented by Native Americans, who domesticated tobacco (Nicotiana rustica). Native Americans were also one of many groups that domesticated the Calabash Gourd (Lagenaria siceraria) for containers and food, but I find no records of their using gourds as pipes. Instead, South Africans seem to have placed a meerschaum bowl inside a curved calabash holder to create the classic calabash pipe, which became a fad when adopted by King Edward VII. This is now associated with Sherlock Holmes because it is a large but light pipe easy to clench between your teeth while delivering lines on stage. But, its use postdates the naming of the Pipevine, Aristolochia macrophylla, which I will sadly concede was named in recognition of its floral form matching clay or meerschaum pipes, not Sherlock Holmes’ calabash.


The big-leaved pipevine was commonly planted in North America a century or two ago, to shade a porch or verandah and give partial privacy. The large green leaves grow exuberantly and the peculiar fly-pollinated flowers provide sculptural interest. The leaves drop in the fall, allowing winter light to reach the porch.

But it’s not for its fly pollinators that I recommend this native vine to gardeners. Instead, its third merit to me is the fact that its leaves are the sole food the caterpillars of the beautiful Pipevine Swallowtail, Battus philenor, will eat.

Battus philenor. John Abbott, 1797

There are many pipevine species in North America and the Pipevine swallowtail likes all of them. Pipevines make a toxin, aristolochic acid, that deters herbivores. But the swallowtail caterpillars take it up and store it, the same way monarch caterpillars store cardiac glycoside from milkweed leaves. The adult swallowtails also taste bad to birds.

Around the world there are many swallowtail species whose caterpillars eat pipevine plants, and share the unpalatability to birds, but the Pipevine swallowtail is our only member of the group. But although it is relatively rare, you will see other swallowtails and unrelated butterfly species that mimic the Pipevine swallowtail. This is an example of what is called Batesian mimicry, where the mimic species gets the benefit (avoiding being eaten by birds) without the cost (methods to handle and store the toxic compounds). The Viceroy butterfly is a Batesian mimic of the Monarch, and the Spicebush swallowtail is a mimic of the Pipevine.

So, from pipes to spice we go!

Spicebush swallowtail - Benny Mazur, CC by SA 2.0

Several native shrubs have the common name “Spicebush”, but here we’re interested in Lindera benzoin, which gets the common name from the aromatic fragrance of its leaves. Lindera grows in
partial tree shade but blooms more abundantly early in spring if it gets some sunlight. The dainty yellow-green flowers don’t make a huge show but are pleasant when winter is ending. This native Carolinian forest shrub should be used more in our parks and ravines, so we can enjoy the Spicebush swallowtails that will come to it.

I’m writing this during the winter holiday, when of course spiced wine has been popular since the time of the Romans. So I can’t resist a spicy diversion. In 1,390 a mediaeval cookbook (by "the chief Master Cooks of King Richard II") gave this recipe for Ypocras: “Pur fait Ypocras …grinding together cinnamon, ginger, galangal, cloves, long pepper, nutmeg, marjoram, cardamom, and grains of paradise ("spykenard de Spayn", rosemary may be substituted). This is mixed with red wine and sugar”. I have read of this drink as “hippocras” - after steeping the spices in the sweetened wine for a day, the spices are strained out through a conical cloth filter bag called a manicum hippocraticum or Hippocratic sleeve (originally devised by the 5th century BC Greek physician Hippocrates to filter water).

"...we will discuss your affairs this very afternoon,
over a Christmas bowl of smoking bishop, Bob!"

Ebenezer Scrooge offered Bob Crachit a variant on hippocras called smoking bishop which was popular in 19th century England.




But what are we to do if we want native tastes in our holiday drinks? If you are lucky enough to have a male and female spicebush plant, the berries from the female can be used as spice. If you don’t have berries, the twigs and leaves can be steeped to make a tea. When my bush is bigger, I shall make this and call it “swallowtail tea”!

Hildegarde v. Bingen,
by W. Marshall

Some people enjoy hopped ales more than spiced wines. The seed clusters of the hopvine have been used in beers in Germany at least since renowned herbalist, mystic, abbess, and composer Hildegarde von Bingen wrote of them in the 11th century AD.

Giant Swallowtail near Ottawa - Gordon Robertson

When Europeans arrived here, they found shrubs and small trees whose seed clusters looked just like hops, and named them Hop Trees (Ptelea trifoliata). They grow wild along the Lake Erie shore in places like Point Pelee and Turkey Point parks, but with climate warming now survive Toronto winters. The seed pods are more decorative than the flowers, but I want to see them in our cityscape because the caterpillars of our largest butterfly, the Giant Swallowtail Papilio cresphontes eat the leaves. I wrote about hoptrees and giant swallowtails last fall.


I’ve taken us from pipes to spice to hops, with some deviations on the way. But what about paws? Admittedly, I am dreaming about getting a puppy in the new year, but here I’m thinking of the delicious and underused native Carolinian fruit tree, the Pawpaw or Asimina triloba. Pawpaw is now being grown in Toronto by connoisseurs who value the wonderful fruit. It fits into this article because of the beautiful native Zebra swallowtail  butterfly, whose caterpillars eat only pawpaw leaves.

Pawpaw flower - Krzystof Ziarnek CC-by-SA 4.0

I first saw these  lovelies during my two year exile in Virginia. The Palace of Neurons where I worked had large grounds running down to the Potomac River. In the moister soil near the river, Pawpaws grew in abundance as an understory tree. That’s plant geek for “grows OK mostly in the shade of big trees”. Pawpaw trees are very rare in Carolinian Canada, but we know our indigenous peoples used the fruit, because there are little-known groves of pawpaw trees next to some of the canoe trade routes inland from Lake Erie. In the spring, male Zebras patrolled streams leading to the Potomac Pawpaw groves, looking for newly emerged females. In summer, second brood adults perched on blue pickerelweed flowers (Pontederia) in the

Zebra Swallowtail - Clement Kent, CC by SA 3.0

ponds.

Given the delicious fruit and the spectacular butterfly, we definitely needs more “paws” in the ravines running down to High Park and in partly shaded places in our gardens.

There are two gardening notes to the pawpaw, though. It needs to be cross-pollinated so two genetically different trees should be planted within half a block or less of each other. And, it suckers from root runners. My trees do this but I find pruning the suckers at ground level once or twice a year controls them nicely. For a very nice dive into pawpaws, go here.


So, Dear Reader, that’s my tale: of Hops and Spice, Pipes and Paws.

Clement Kent

p.s. if you missed the previous post on Project Swallowtail, please give it a look. Project Swallowtail will be increasing the host plants above in order to have more of these beautiful butterflies.

Project Swallowtail!

Giant Swallowtail - Gordon Robertson

Today  it's my pleasure to pre-announce Project Swallowtail!

Zebra Swallowtail - Megan McCarty

This initiative to increase pollinator habitat in a large chunk of downtown west Toronto is led by WWF Canada in collaboration with many other groups, including my own Horticultural Societies of Parkdale and Toronto.






Blue dots on the map show just some of the gardens and Block Ambassadors already included.

Kathy's Garden, Stanley Park - Clement Kent

What are we going to do? Simply, we're going to help your block get a much higher density of pollinator-friendly plants over the next several years, with the goal of greatly increasing pollinator numbers and health. We want to do this in a way that allows birds, butterflies, and bees to move
freely for park to park and home to home. And, we'll be using some locally rare but very visible species such as the swallowtail butterflies shown above to make it easy to see when your block has become a hotspot of pollinator diversity.

LEAF Young Urban
Forest Leaders

We're also going to involve local kids and young adults in several ways. Mobile apps to help them identify plants and pollinators will be rolled out, with awards going to young pollinator experts.

Perhaps your block will become part of a neighbourhood where collaborator LEAF helps young naturalists learn about, map, and plant an urban forest?

Or maybe your or your neighbours' kids will go to High Park to learn about native plants and animals from H.P. Nature?

Block Ambassadors

Would you like to help us enrich your block for pollinators? We need Block Ambassadors! You don't need to be a gardener or a naturalist - just someone who likes talking with neighbours and promoting this project. We'll ask you to donate a few hours a month of your time to helping your neighbours get the plants and the help they need. You can reach us at clementfkent@gmail.com [this address will change very soon now!] See our map of ambassadors in your vicinity.


Collaborators:

• World Wildlife Fund Canada
• Horticultural Societies of Parkdale and Toronto
• Pollinator Partnership Canada
• David Suzuki Foundation
• High Park Stewards
• LEAF
• City of Toronto Parks and Forestry
• Business Improvement Associations
• Toronto Botanical Garden
• North American Native Plant Society