Success! A giant swallowtail butterfly emerged from the pupa that had overwintered on our front porch. It was late afternoon on May 27th when Greg discovered the adult butterfly as he walked in the front door. We grabbed the camera and ran to the front porch. We observed the butterfly closely for about 10 minutes before it took flight and headed for a tree in our garden. It was in the tree in the same place the next morning, but then it flew off. Where did it go? Did it find a mate? Did it survive to reproduce? Are its caterpillars now happily munching away on leaves of hoptree (or prickly ash, its only other food plant in southern Ontario)? One thing is certain, we have planted more hoptree! And in so doing, we have created more native habitat for the giant swallowtail butterfly in southern Ontario.
A Giant Story
Posted by NM Zitani and RG Thorn; 4 April 2011 Film editing by David Mills
It was 6:30 pm, Wednesday
21 July 2010, 12 months after we had planted the food of her caterpillars in
our biodiversity garden in London, Ontario.
There she was: enormous, and unmistakable, dark brown with yellow markings,
a female giant swallowtail butterfly laying eggs on hoptree in our front
yard. I couldn't believe my
eyes, as I never really expected to see a giant swallowtail on our property, let alone so soon
after incorporating the food plant of the caterpillar into our garden. But that is exactly what we had in mind
when we planted hoptree, Ptelea trifoliata in our garden – to attract and provide habitat for Canada's largest native butterfly.
We were getting our youngest ready
for bed when Greg yelled out "giant swallowtail on the hoptree!" I
grabbed the camera and ran outside, with our older son trailing close behind.
Against some garden designer's principles, we had planted a
single smaller specimen of hoptree just across the path from our front
door. (Mighty convenient for spotting and filming butterflies!) We
watched the female butterfly for about 1/2 hour, as she alternately
oviposited (laid eggs) and flew in broad circles high above our
property, often disappearing from view. (We captured the event in a video, part of which is shown below). Once she had departed for
good, we counted about 20 eggs on leaves (one egg per leaf) scattered around the plant.
In a few days, much to the delight of our boys, we were the proud caretakers of several bird-poop mimicking caterpillars! The remarkable caterpillars of the giant swallowtail butterfly closely resemble bird droppings when they are young. To complete their dark brown and yellowish mottled coloring they have a glossy finish, so that they appear wet - just like a fresh bird poop on a leaf - as they attempt to trick birds, their primary predators with ultra keen vision. At first we found about 3 caterpillars in total, and that quickly shrank down to one as they were picked off by birds and other predators. By 11 August the caterpillar was plump and nearly full-grown, and had lost its glossy, wet-looking appearance. "It no longer looks like bird poop" our older son aptly commented.
The giant swallowtail butterfly belongs to the insect family Papilionidae, commonly called the swallowtail family. All swallowtail caterpillars possess an organ called an osmeterium, and it is one of the characteristics that unites all members of the swallowtail family. The osmeterium is a brightly colored (red, in the giant swallowtail), fork shaped, eversible gland located just behind the head. When a swallowtail caterpillar is threatened it will evert this gland extremely quickly, and studies have shown that birds become startled at the sudden appearance of it. If that were not enough, the gland also emits a very foul odor to further deter predators. (The video below shows our son gently prodding the caterpillar, and the caterpillar everting its osmeterium in defense. During the last seconds of the film you see and hear our son's response to the foul odor).
By 18 August, 28 days after the eggs were laid, our giant swallowtail had reached the next stage of metamorphosis, the pupal stage. The pupa of a butterfly is called a chrysalis, and it is "naked" meaning there is no protective silken cocoon surrounding it, as in most moths, and most wasps, and other insects that can spin silk. When you look at a butterfly chrysalis, you are looking directly at the exoskeleton, or outer surface of the animal. The giant swallowtail pupa mimics a twig (or curled up old leaf) in an attempt to camouflage itself. What look like two pieces of string connecting the pupa to the twig are silk threads. Those "strings" are made by the caterpillar. Prior to pupating, the caterpillar attaches itself securely to a plant part by these silk threads - called a silk girdle.
Our giant swallowtail pupa spent the winter tucked away in a protected corner of our front porch. It remains to be seen whether the adult butterfly will emerge once the warmer weather sets in. If it does, you can be sure you'll hear about it -- we'll keep you posted!