The monarch butterfly (Danaus plexippus) is one of the most recognizable and well-known butterfly species in North America. With its bright orange wings marked by black veins and white spots, the monarch is unmistakable. However, there are some other butterfly species that bear a close resemblance to the monarch and are often confused with it by casual observers. One such lookalike is the blue butterfly species that goes by the common name ‘Eastern tiger swallowtail’.
The Eastern tiger swallowtail (Papilio glaucus) is a large, brightly colored butterfly that shares some visual similarities with the monarch. Like the monarch, it has dark black veins crossing its wings and its wingspan can reach up to 4.5 inches. However, upon closer inspection, there are several key differences that distinguish it from the monarch. While the monarch has orange wings, the Eastern tiger swallowtail has wings that are yellow or pale green. Females of the species can also exhibit a special blue morph of the wings, leading to it sometimes being mistaken for the monarch.
In this article, we will take a closer look at the blue morph of the Eastern tiger swallowtail and understand what makes it so similar to the iconic monarch butterfly. We will explore its life cycle, habitat, distribution and behavioral patterns and also touch upon ways of differentiating it from a true monarch butterfly.
Life Cycle and Metamorphosis
The Eastern tiger swallowtail goes through a complete metamorphosis during its life cycle, just like all butterflies. The cycle begins when a female butterfly lays her eggs, usually singly on the leaves of the caterpillar’s host plant. The larva or caterpillar hatches from the egg and begins feeding voraciously on the leaves. It sheds its exoskeleton several times through a process called molting as it grows bigger. After reaching full growth, the caterpillar attaches itself to a perch using silk and enters the pupal stage. The pupa undergoes radical changes in this stage, transitioning into the winged adult butterfly. After 1-2 weeks, the adult butterfly emerges from the pupal case.
The female Eastern tiger swallowtail prefers laying her eggs on trees and plants of the Magnolia family or the tulip tree. Some commonly used host plants are the tulip tree (Liriodendron tulipifera), sweetbay (Magnolia virginiana), and wild black cherry (Prunus serotina). The caterpillars are green with two black, yellow and blue eyespots on their thorax. They can reach up to 2 inches in length when fully grown.
The most striking feature of the Eastern tiger swallowtail is its ability to exhibit color dimorphism. normal females are yellowish-green with four black tiger stripe markings, while males are yellow with four black stripes and a wash of blue scaling. However, some females may be darker black or exhibit a dark blue iridescence over parts of the wing instead of the normal green color. It is this blue female morph that most resembles the monarch butterfly.
Distribution and Habitat
The Eastern tiger swallowtail is widely distributed across eastern North America from Ontario and Quebec to as far south as northern Florida and the Gulf Coast. It is found commonly along the eastern United States in deciduous forests and areas with sufficient vegetation.
Unlike the monarch which migrates long distances, the Eastern tiger swallowtail does not migrate and can be spotted across its range from spring to fall provided the climate is mild. It prefers open woodlands, streams, parks and suburban areas with an abundance of flowering plants. Adults feed on the nectar of these flowers, while caterpillars feed on the leaves of host trees.
Some of the natural habitats of the Eastern tiger swallowtail include:
- Deciduous broadleaf forests
- Riparian zones along streams and rivers
- Parks and gardens
- Fields and meadows
The butterfly ranges from southern Canada through the eastern and central United States. Its distribution overlaps extensively with the monarch’s summer breeding range, leading to confusion between the two species.
Appearance and Markings
Let us take a closer look at the physical appearance of the blue female Eastern tiger swallowtail and how it mimics the monarch:
Size: With a wingspan reaching 3.5 to 4.5 inches, the Eastern tiger swallowtail is similar in size to the monarch butterfly.
Wing color and pattern: The blue morph female has velvety dark blue wings. From a distance, this can resemble the orange hue of the monarch. The black tiger stripe markings are also reminiscent of the monarch’s black veins.
Wing shape: Both butterflies have elongated forewings and rounded hindwings, leading to a similar overall wing shape and profile in flight.
Spot patterns: The Eastern tiger swallowtail exhibits rows of yellowish spots along its hindwings and leading edges of the forewings. In some angles, these can look similar to a monarch’s white spots.
Antennae: Both species have long, thin antennae with clubbed tips which enhance their resemblance.
However, upon closer examination there are a few ways to reliably tell the two species apart:
- The Eastern tiger swallowtail lacks the thick black borders seen on a monarch’s wings.
- The orange color of the monarch is brighter compared to the dark blue of the Eastern tiger swallowtail.
- The yellow spots on the Eastern tiger swallowtail are larger and more elongated in shape compared to the monarch’s uniform white dots.
- The Eastern tiger swallowtail’s body is mostly black, while the monarch has an orange/brown body.
Behavior and Diet
Adult Eastern tiger swallowtails exhibit feeding behaviors similar to monarchs and have comparable diets. They fly amongst vegetation visiting flowers and gathering nectar through their long proboscis. They are drawn to flowers with vivid colors and prefer lilacs, milkweeds, dogbanes, and thistles. The adults get most of their nutrition from these liquid nectar meals.
Eastern tiger swallowtails lead solitary lives and do not gather in congregations like monarchs. The males will patrol territories looking for mates and exhibit a unique behavior called puddling, where they gather at wet mud and dirt to suck up nutrients and minerals. The females spend their time looking for suitable host plants for laying their eggs.
At night, Eastern tiger swallowtails take shelter individually on high branches, tree hollows or dense vegetation. They tuck their wings together upright when at rest. Overall, their behaviors are not dramatically different from monarchs in the wild.
Threats and Conservation
The Eastern tiger swallowtail is a common and widespread butterfly that is not currently considered threatened. With its ability to utilize a diverse range of flowering plants and trees, it is not as vulnerable to habitat loss as specialized species. The caterpillars do face heavy predation pressure from birds and small mammals, but this is offset by the female’s high reproductive rate.
However, the Eastern tiger swallowtail does face some conservation issues in certain parts of its range:
– Pesticide use can impact caterpillars feeding on agricultural or suburban plants
– Fragmentation and loss of riparian habitats through river damming and channelization
– Tree removal in forests disrupts breeding and nectaring sites
– Climate change may affect host plant distribution in the future
– High deer browsing pressure in some areas decreases caterpillar survival
Overall the Eastern tiger swallowtail is resilient and remains common throughout most of its range. It has not experienced the severe population declines that monarch butterflies have faced in recent decades. But habitat conservation and protection from pesticide drift can still help this beautiful species. It serves as an important pollinator as well as food source for birds and small predators. Maintaining biodiversity will allow this charismatic butterfly to continue gracing eastern forests for generations to come.
Conclusion
The blue morph of the Eastern tiger swallowtail provides a stunning example of mimicry in the insect world. With its similar size, wing shape, markings and flight patterns, it resembles the toxic monarch butterfly to predators. This affords it some protection, though Eastern tiger swallowtails are not toxic themselves. Beyond coloration, the two butterflies also share similarities in life cycle, habitat preferences, and feeding behaviors. But upon closer inspection, the differences in wing patterning and colors provide reliable ways to distinguish the Eastern tiger swallowtail from the monarch. Understanding these delicate evolutionary adaptations allows us to better appreciate the interconnectivity of plant and animal life. Whether it is an orange monarch or blue tiger swallowtail flitting amongst the summer wildflowers, these butterflies add an element of wonder and beauty to the natural riches around us.
References
Brock, J. P., & Kaufman, K. (2003). Butterflies of North America. Boston: Houghton Mifflin.
Glassberg, J. (1999). Butterflies through Binoculars: The East. Oxford University Press.
Opler, P.A., & Malikul, V. (1992). A Field Guide to Eastern Butterflies. Peterson Field Guides.
Wagner, D.L. (2005). Caterpillars of Eastern North America. Princeton University Press.
