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COLUMN: Sharing the water with swallowtails


I was fishing a few weeks ago with the hope of intercepting a few sea trout. It was a hot day, and the water was low, so the fishing was slow.

As I fished down the river I was soon distracted by the sight of large numbers of butterflies clustered together on the sand at the edge of the water. After seeing several groups I decided to get a closer look. I don’t know a lot about butterflies but I thought these were swallowtails because of their yellow and black colour along with the shape of their wings. Swallowtail wings have a long tail on each side which resembles the wing of a swallow – hence the name.

I was curious why the butterflies were gathered together in large groups and I thought it may have something to do with mating so, when I got home, I did some research and discovered several facts that I wasn’t aware of before.

One was that, while there are several species of swallowtails, here in Nova Scotia, the ones I saw are a distinct species known as the Canadian swallowtail. This species ranges from Newfoundland to Alberta and as far north as the Arctic Circle. The second was that the behaviour I observed actually has a name, mud puddling, and is common among a variety of butterflies and other insect species. It involves butterflies gathering in large numbers together around a puddle, wet mud or sand. There they drink to get nutrients, such as salts and amino acids, they require to complete their life cycle.

Swallowtail butterflies don’t live very long. An adult lives for about one month before it mates and lays its eggs to begin the cycle over again. Butterflies have four stages in their life cycle. It begins when the female lays her eggs individually on plants which can provide nourishment once the eggs hatch. In the case of swallowtails favourite tree species include poplars, willows, wild cherry and apple. The eggs are laid on south-facing leaves where the warming sun speeds up development. The eggs hatch into the larval form, which we know as a caterpillar.

Most people have probably seen swallowtail caterpillars without realizing what they were. They are green in colour and have four yellow dots and two false eyes which are designed to scare away predators. The caterpillar feeds on tree leaves until it forms a nest by folding over a leaf and spinning a cocoon with silk it produces. From there it enters the pupae stage where it develops and hatches into an adult. The process from egg to emerging adult takes about a month so swallowtails rear one brood per year.

Butterflies have a variety of mechanisms to survive the winter. Some species over winter in the egg stage, others as caterpillars and some, such as monarch butterflies migrate to warmer climates. Swallowtails survive our winter in the pupae stage and begin emerging as adult butterflies when the weather warms up in May.

While the caterpillar actively feeds on leaves adult butterflies don’t feed – they drink. They have a long tube in their throat known as a proboscis and they insert this tube into flowers to drink nectar, their main food source. While swallowtails mainly feed on wild plants you can attract them to your garden with plants ranging from lilacs and zinnias to butterfly bush and purple coneflowers.

While I came home without any trout it was still a great trip and I gained some new knowledge of, and appreciation for, swallowtail butterflies.


Don MacLean is an outdoor writer and biologist who lives in Pictou County.

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