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