This month’s article is the second in a series of articles on host plants for butterflies and moths that I began last month. I started with two common butterflies in my garden, the Black Swallowtail (Papilio polyxenes) and the Giant Swallowtail (Papilio cresphontes). In today’s article I will look at two more swallowtail butterflies that I regularly see in my southwestern Ontario garden. As before, I will provide photos of the butterfly and its caterpillar (and egg, if I have a photo), as well as photos of some of its host plants along with some basic facts about growing these plants.  

Spicebush Swallowtail (Papilio troilus) 

Often (and easily) confused with last month’s Black Swallowtail, the Spicebush Swallowtail is a rare visitor in my garden, despite my having two large Spicebushes, a couple of Tulip Trees and a Sassafras tree, all of which are its host plants in the southern Great Lakes region. 

Like the Giant Tiger swallowtail, the young caterpillar of the Spicebush Swallowtail looks a lot like a bird dropping, thus discouraging predation by birds. However, as it outgrows its skin and gets larger and larger, it takes on a bright green colour and develops two large eye-spots, supposedly mimicking a snake. In its final instar, it tends to be bright yellow or orange, sometimes even a reddish orange colour. 

The adult Spicebush Swallowtail nectars on a wide range of flowering plants, including asters, milkweeds, Purple Coneflower, and thistles. It is a large butterfly, with a wingspan of 3¹/₂  to 5¹/₂”.  

Northern Spicebush (Lindera benzoin) 

• Lindera benzoin, sometimes called Wild Allspice, is a shrub in the Laurel family. It is typically found in moist, rich forests as an understory shrub, growing from 5-15 feet tall (in my gardens, the height seems directly correlated to average soil moisture). This lovely shrub has early spring yellow flowers around the same time as the non-native – and useless to our butterflies – Forsythia. You supposedly need a male and a female plant to get fruit, but both of my shrubs produce berries yet I have yet to find another Spicebush in my neighbourhood! 

• If you have part to full shade and moist to average soil, this shrub is a must for your garden. The leaves have a lovely spicy fragrance when crushed, and a tea can be made from the twigs and leaves. Both green (unripe) and red (ripe) berries offer distinct tastes: green berries are sharp, lemony, and peppery, while red berries are sweeter, reminiscent of allspice. The berries can be used fresh or dried, with drying intensifying the flavor and prolonging their shelf life. 

Tulip Tree (Liriodendron tulipifera) 

• Liriodendron tulipifera is a magnificent tree – in the forest it grows tall and straight and can reach heights of 60-90 feet. Open-grown, it makes a wonderful shade tree.  But probably its most notable feature is the large, yellow and green tulip-like flowers it produces each spring.  

• Tulip Trees prefer full or partial sun, mesic conditions, and fertile soil that is loamy or silty. It is a fast grower and can produce flowers in less than 10 years. (In my mesic, silt-loam soil in part shade, my tulip tree reached about 40 feet tall and 18” across (dbh) in less than 15 years!) But, as with most fast-growing trees, the branches are a bit brittle and susceptible to ice and windstorm damage. 

Sassafras (Sassafras albidum) 

• A medium-sized tree (50-65 feet tall), Sassafras albidum is probably best known for it historic use for flavouring root beer. However, its use for this commercially was banned when it was shown that large doses of the active ingredient (safrole) caused liver damage and was linked to some cancers.  

• The leaf shape can be quite variable, from a simple leaf to a “mitten” to a “trident”, and the leaf shape and their beautiful red and gold fall colours make this an interesting specimen in the garden. Like the Spicebush, this tree is typically dioecious, having male and female flowers on separate trees. This is a colony forming tree and, if allowed to grow unchecked, will send up root sprouts and soon form a grove.  

• It will grow in just about any loose, moist soil but it needs full sunlight for good growth. It seems to be a favourite of the invasive Japanese beetles in my garden, which often do a lot of cosmetic damage to the leaves, though it hasn’t seemed to impact the health of the tree. 

Eastern Tiger Swallowtail (Papilio glaucus) 

The Eastern Tiger Swallowtail is the most common swallowtail butterfly in my garden, but they are quite territorial so I usually only see one resident – any other Tiger Swallowtails that pass through are harassed until they move on. They will even chase off other species of butterfly, and I once saw one chase after a sparrow (a move I thought rather brave – or foolish – as the bird could have quickly turned the tables).  

These large (up to 5¹/₄” wingspan) bright yellow butterflies are hard to miss. Their preferred host plant is the Tulip Tree (Liriodendron tulipifera), but they will also use the Hop Tree (Ptelea trifoliata). If neither of these is available, they have also been known to use cherry trees (such as the Wild Black Cherry – Prunus serotina) and ash trees (Fraxinus spp.). 

Tulip Tree (Liriodendron tulipifera) – see above 

Hop Tree (Ptelea trifoliata)  

• The Hop Tree goes by many common names – Wafer Ash, Stinking Ash, Swamp Devil’s Bit, Water Ash, Wing Seed and even Shrubby Trefoil. This is a small tree/ large shrub, getting 15-20 feet tall and spreading just as wide. It likes just about any kind of soil in full sun to full shade. It even makes a good potted shrub – just make sure your pot is large enough. The Hop Tree is monoecious, often producing male, female, and perfect (bisexual) flowers on the same shrub. 

• The first time my Hop Tree flowered (in June), I couldn’t figure out where the lovely fragrance was coming from. Once I did, I regularly altered my path so I could come near the blossoms for a whiff of perfume. But it must be one of those fragrances (like the taste of Cilantro for some) that you either love or hate – how else would it get the common name Stinking Ash?!? 

Further Reading

If you’d like to know more about the differences in our Swallowtail butterflies, there are two great sites with lots of comparison images at https://www.butterfliesathome.com/swallowtail-butterflies.htm and https://www.facebook.com/photo.php?fbid=684652250358733&id=100064418930419&set=a.558096469680979.

Who doesn’t love to see a majestic butterfly flit through the garden, alighting on newly opened flower buds for a sip of nectar, then watch as it explores what else you have to offer. If you’re really lucky, you may even get to see it lay an egg or two on the underside of a leaf. Although most folks do know by now the relationship between Monarch Butterflies and Milkweed, surprisingly I met someone a few weeks ago that saw monarchs nectaring on his Purple Coneflower and wondered why he never saw them laying eggs on it! He didn’t realize that they ONLY lay their eggs on members of the Milkweed family. 

Monarchs aren’t the only butterflies (or moths, for that matter) that have very particular tastes. Although some species of Lepidoptera are generalists – meaning their caterpillars will eat many different kinds of plants, what a lot of folks don’t realize is that most butterflies and moths do not lay their eggs on just any plant. They require very specific species of plants if they are to successfully multiply their numbers.  

This month’s article will be the first in what I hope will be a series of articles about host plants – which plants host which butterflies and/or moths – and a brief description of what you need to grow those plants to make your yard a nursery for many beautiful butterflies and moths. I shall start with my own favourite butterflies, the swallowtails. 

Swallowtail Butterflies 

In the southern Great Lakes region, we are home to 9 species of Swallowtail Butterfly, according to Rick Cavasin  (https://www.ontariobutterflies.ca/families/Papilionidae) one of which – the Midsummer Tiger Swallowtail – he indicates has only recently been described. In today’s article I will cover the two most common ones that I regularly see in my southwestern Ontario garden. I will provide photos of the butterfly and its caterpillar, as well as photos of some of its host plants along with some basic facts about growing these plants. Over the coming months I will look at a few more of the swallowtails, then perhaps go on to some of our other butterflies, if sufficient interest exists. 

Black Swallowtail (Papilio polyxenes)  

This black beauty is a challenge to photograph because it rarely sits still. Even while nectaring its wings are constantly aflutter. The caterpillar of this butterfly feeds on plants in the carrot family. Many vegetable gardeners are accustomed to seeing it on their dill and parsley plants, and even on their carrots or celery, and if you don’t mind sharing your produce, this is a great way to attract them. 

The native host plants for Black Swallowtail Butterflies include Golden Alexander (Zizia aurea), Cow Parsnip (Heracleum maximum), Purplestem Angelica (Angelica atropurpurea), Sweet Cicely (Osmorhiza claytonia) and Canadian Honewort (Cryptotaenia canadensis). 

Golden Alexander (Zizia aurea) 

• Zizia aurea is a full to part sun perennial that likes moist to dry, sand to clay soils. It is an early flowering plant in the garden, with blooms starting in early May and often blooming right through to the end of June. (On a personal note – the first year I grew just a single Golden Alexander plant, I had 7 Black Swallowtail caterpillars on it!) 

Cow Parsnip (Heracleum maximum) 

• Heracleum maximum is the tallest member of the carrot family in North America, often reaching heights of 6-8 feet. It is a relative of Wild Parsnip and Giant Hogweed, and like those plants its sap can cause sun rashes or blisters. It grows in full to part sun, in just about any moist but well drained soil. 

Purplestem or Great Angelica (Angelica atropurpurea) 

• Angelica atropurpurea is another giant in the garden, often getting up to 7 feet tall or more. This short-lived perennial likes full to part sun and wet to moist clay or loamy soil, or sandy soil with lots of decaying organic matter.  As with Cow Parsnip, if you choose to grow this plant be careful to avoid getting the sap on your skin. 

Sweet Cicely (Osmorhiza claytonii), Aniseroot (O. longistylis) 

• Osmorhiza claytonia and O. longistylis are plants for full to part shade. They tolerate most soil types and like average moisture soils. They get about 2 feet tall and bloom in May and June.   

Canadian Honewort (Cryptotaenia canadensis) 

• Another shade plant, Cryptotaenia canadensis, starts flowering in June and can continue right through to September, and though its flowers are quite small and delicate they often put on a lovely show because of the sheer number of blossoms. This perennial can get up to 2 or even 3 feet tall in average moisture, rich, loamy soil. 

Giant Swallowtail (Papilio cresphontes)  

The Giant Swallowtail gets it common name for a good reason – with a wingspan up to 4½ inches (113 mm) – it is the largest butterfly in Canada. Its caterpillar, unlike the colourful caterpillar of the Black Swallowtail (which the uninitiated often confuse for a Monarch caterpillar), looks exactly like a bird dropping on a leaf. Its disguise is so convincing that these caterpillars don’t even bother to hide under the leaf. You will almost always find them sitting on the top of the leaf, as if the bird had just pooped and flown on. 

The Giant Swallowtail’s host plants are mostly members of the citrus family – the leaves of orange, lemon, lime and grapefruit trees. Fortunately, we have two species that it uses here in the southern Great Lakes region – Hop Tree and Northern Prickly-ash (both of which member of the citrus family). The fact that Prickly Ash is related to oranges is obvious as anyone who has tasted the berries can tell you – it’s like biting into concentrated orange rind. 

Hop Tree (Ptelea trifoliata)  

• The Hop Tree goes by many common names – Wafer Ash, Stinking Ash, Swamp Devil’s Bit, Water Ash, Wing Seed and even Shrubby Trefoil. This is a small tree/ large shrub, getting 15-20 feet tall and spreading just as wide. It likes just about any kind of soil in full sun to full shade. It even makes a good potted shrub – just make sure your pot is large enough. The Hop Tree is monoecious, often producing male, female, and perfect (bisexual) flowers on the same shrub. 

• The first time my Hop Tree flowered (in June), I couldn’t figure out where the lovely fragrance was coming from. Once I did, I regularly altered my path so I could come near the blossoms for a whiff of perfume. But it must be one of those fragrances (like the taste of Cilantro for some) that you either love or hate – how else would it get the common name Stinking Ash?!? 

Northern Prickly-ash (Zanthoxylum americanum) 

• Northern Prickly-ash is a very thorny shrub that can get 15-20 feet tall, though the only place I’ve seen it in the wild (the alvars of Prince Edward County, near Kingston, Ontario) the shrubs were typically around just 5-7 feet high. Not a great choice for a small yard as it can spread aggressively by root suckers, but these can be controlled by either pruning them as they appear, or by planting the shrub in a barrel sunk into the ground.  

• Prickly-ash does best in full sun, in well drained, average soils. It produces small, inconspicuous green flowers in the spring, but these are beautifully aromatic and attract many bees. Even the leaves have a lemony smell when crushed. In late summer, the fruit ripens to a reddish orange. Another common name for this plant is Toothache Plant, because eating the berries will numb your mouth, but you will need both a male and a female plant to get berries. ` 

Next time: Eastern Tiger Swallowtail and Spicebush Swallowtail