They said she was on her way, and on June 12, there she was - the Giant Swallowtail, floating through the flower beds, the largest butterfly I have ever seen in these parts. I hadn’t heard she was coming so I grabbed a camera to document the find, and a day later a naturalist friend identified her, telling me there had been recent media reports about how this species is moving north.
I didn’t think, when I saw her a few more times, whether she might have special needs, this creature forced northwards by global warming, even though the question of assisted migration is one of my
preoccupations. Then today, I was moving some potted Hop Trees out of a sheltered location close to the potted Northern Catalpas, thinking they all need a bit more space, a bit more sun, so they’re ready to be planted out at some stage.
That’s when I saw it. The poo on the leaf. And then I noticed that the poo, at first glance the poo of a very large bird, in fact had a structure, markings, and evidence of activity: the Hop Tree leaf that supported it was half gone.
A dash to Google confirmed that this is a caterpillar, disguised as a bird dropping. Described as one of the ugliest caterpillars around. This, for one of the continent’s most striking butterflies, the largest in North America, with a wing-span of 6 inches. Although I confess, I don’t find this living facsimile of a feces ugly at all – it’s quite fascinating in its combination of white and brown, with definite markings of a face at one end and, just to be on the safe side, another face at the non-eating end. As if all these deterrents aren’t enough, it appears that when disturbed, these caterpillars deploy a pair of bright red horns and release an unpleasant stench. Perhaps this one was too young, or not disturbed enough, fortunately none of that happened.
Even though I wasn’t expecting the Giant Swallowtail, I was prepared. Insect larvae (caterpillars, in the case of butterflies) are highly specialized when it comes to what they can eat. They need the plant with which they have evolved over millennia - just any old leaves won’t do. That’s a major reason for planting natives – to support the insects that are the foundation of the food chain for our birds and mammals.
The Giant Swallowtail lays her eggs on plants that are members of the Rutaceae family - Common Rue, Orange and Lemon trees, Prickly Ash and Hoptree. Thanks to my interest in Carolinian species that used to have their northern limit on the north shore of Lake Erie, I have a number of Hop Trees on hand. If I hadn’t, the displaced butterfly would have searched the garden in vain for suitable habitat to perpetuate her species. That would have been sad – she moved north because conditions in the more southerly locations where Giant Swallowtails have bred since settlers started keeping records have changed and no longer work for her. But unless we northerners think ahead to provide the plants she needs, her species will decline.
I didn’t get Hop Trees with Papilio cresphontes in mind. My motives were aesthetic; Ptelea trifoliata is a charming little tree with interesting foliage and blooms.
Here’s a description from Kansas writer Lenora Larson, on the North American Butterfly Association
website: “This small, multi-stemmed tree has glossy, dark-green leaves that exude a citrus smell when crushed. Hardy from zones 3 through 9, it grows to 10 feet in light to deep shade, which makes it an ideal understory tree. The slow-growing Hop Tree does not overpower a small urban garden and will happily adapt to containers for an apartment dweller’s patio or balcony. My attempt to prune one into a standard was a dismal failure. It flopped and flailed until I took pity and cut it to the ground so it could re-grow as a multi-stemmed large shrub.”
I’m with Larson on letting this tree be a shrub – I had one trained to a standard when I purchased it at a Guelph Arboretum sale, and it died. The multi-stemmed replacement is much sturdier. But the planted specimen is not the one Madam Butterfly chose to host her progeny. She took to the potted trees in the nursery because, I reckon, of the extra protection provided by the crowded foliage. And perhaps four small trees make more sense than one big one.
I threw some row cover over the lot of them, remembering a previous experience with an amazing caterpillar. The Cecropia – North America’s largest moth - has a caterpillar that is party-coloured – lime-green with orange and blue and red protuberances. It made its appearance on a High-bush Cranberry some years ago and I visited it often, until suddenly one morning, it was gone. I realized it had been down to me to protect it - and I hadn't.
One last visit for the night – it’s still there. And will be tomorrow, I hope…
