Today’s post comes to us from Chris Robinson, Natural Heritage Education Leader at Charleston Lake Provincial Park.
This is a vibrant and colorful time of year at Charleston Lake Provincial Park, with long-lasting sunshine and seemingly endless days. June and July are also when butterfly watching is best!
Some of the most striking butterflies in the park are the tiger swallowtails, known for their large size, distinctive colors and streamer-like “tails” on their hind wings.
These butterflies are aptly named: they are yellow with striking black tiger stripes. You can easily spot them, patrolling along the edges of the forest or searching for nectar from various flowers.
Here at Charleston Lake, we have not one but two types of these stunning “tigers,” the Eastern Swallowtail Tiger and the Canadian Swallowtail Tiger. However, being closely related, it is difficult to distinguish them.
The eastern tiger
The eastern tiger swallowtail, further south, is slightly larger (7-10 cm wingspan) and has a slightly narrower black band on the inner hindwings. Its range extends south to Florida and in Canada it reaches only southern Ontario.
It has two broods, which means there are two generations flying per year. The first flies in late May and June, and the adults of the second generation fly in July and sometimes until August.
The Canadian Tiger
The smallest (5-9 cm) Canadian Tiger Swallowtail It is the northernmost of the two, extending north to the Yukon and south to the US along the Appalachian Mountains.
Its pupae (cocoons) can survive colder winter temperatures than the eastern variety. It only has one generation per year, usually from late May to late June (thus a tiger swallowtail butterfly seen in July or August is almost certainly an oriental butterfly).
The daily routine of a butterfly
As adults, butterflies tend to have a typical daily schedule. In the morning they spend time sunbathing to raise their body temperature and warm up their flight muscles.
Butterflies, like all insects, cannot warm themselves like we humans and other mammals, and rely on the sun to keep them warm. Once warmed, they visit flowers in search of nectar, a source of sugary liquid food.
Once fed, male tiger swallows spend much of the afternoon searching for females. They fly back and forth patrolling the same route, often along streams, roads, or edges of open fields. A male will follow a female he finds and attempt to mate with her. A female who is not interested in mating will close and flatten her wings to prevent him from grabbing her.
A mated female, once warmed and fed, begins the critical task of searching for plants to lay her eggs, such as cherry and ash trees here in the park (although the less demanding Canadian tiger swallowtail also lays her eggs in poplars and willows ).
It prefers to lay its eggs on exposed leaves on the south side of trees and less than 2.5 m high, presumably for increased warmth from the sun and less exposure to wind. Higher temperatures accelerate the development of caterpillars emerging from the eggs, which is essential. Faster development means less exposure to bird predators or parasites.
Tiger swallowtail caterpillars They are very tasty to birds, so they rely on scheming ways to avoid predators. In the initial stages of growth, caterpillars mimic the appearance of bird droppings to help avoid detection. In the later stages, the caterpillars are green to blend in with the green leaves they feed on.
These caterpillars have huge false eyes that make them snake-like and more intimidating, potentially warding off predators. They also have a special forked, tentacle-like appendage (unique to swallowtails) that emerges from behind their heads when disturbed. This appendage emits a foul odor and is believed to be a defense against predators, particularly ants.
While tiger swallowtail caterpillars rely on camouflage, this is not the case for the brightly colored adult butterflies. To avoid the many hungry birds out there, adult Tiger Swallowtails use clever tricks. Each hindwing has a pattern of lines that converge on the inner wing, where there is a blue spot and a long, serpentine-shaped “tail.” This creates the appearance of a “false head” on the underside of the hind wings (the point furthest from the real head) with “eyes” (the blue spots) and “antennae” (the tails). A potential predator may be attracted to this false head, rather than the real head and body.
It is not unusual to see tiger swallowtails with sections of their hindwings missing where their tails once were. A butterfly can live with a damaged wing, but it is less likely to survive an attack on its head and body. Keep an eye out for butterflies with damaged hind wings and beak-shaped teardrops.
A sight to be seen
Another fascinating aspect of the life of the tiger swallowtail is their tendency to congregate in puddles or wet areas in large groups (hundreds of them!) jostling for position. Tiger swallowtails seen in puddles will almost always be male.
But why only men?
Well, males look for salts in the moist soil around puddles, as sodium is naturally low in most plants that butterfly caterpillars feed on. Adult males, in turn, pass sodium to females in a spermatophore, a large “nuptial gift” (weighing up to half the weight of a male) that is placed on the female during mating. Females need sodium to produce eggs. Look out for these “puddle clubs” of congregating males, as they are quite an extraordinary sight!
Eastern and Canadian tiger swallowtails are two of the 70 species of butterflies recorded in Lake Charleston Provincial Park alone, and two of the most recognizable.