Papilio glaucus, the eastern tiger swallowtail, is a species of butterfly native to eastern North America. It is one of the most familiar butterflies in the eastern United States, ranging north to southern Ontario, Canada, and is common in many different habitats. It flies from spring until fall, during which it produces two to three broods. Adults feed on the nectar of many species of flowers, mostly from those of the families Apocynaceae, Asteraceae, and Fabaceae. P. glaucus has a wingspan measuring . The male is yellow with four black "tiger stripes" on each forewing. Females may be either yellow or black, making the females dimorphic. The yellow morph has similar coloring to the male, but with a conspicuous band of blue spots along the hindwing; the dark morph is almost completely black.
The green eggs are laid singly on plants of the families Magnoliaceae and Rosaceae. Young caterpillars are brown and white; older ones are green with two black, yellow, and blue eyespots on the thorax. The caterpillar will turn brown prior to pupating. It will reach a length of . The chrysalis varies from a whitish color to dark brown. Hibernation occurs in this stage in locations with cold winter months.
The eastern tiger swallowtail is the state butterfly of Alabama (as well as state mascot), Delaware, Georgia, North Carolina and South Carolina, and is the state insect of Virginia.
Description
thumb|left|Dorsal and ventral sides. 1. dorsal male; 2. dorsal female; 3. dorsal female (dark morph); 4. ventral male; 5. ventral female; 6. ventral female (dark morph)
The wingspan ranges from Males are yellow with four black "tiger stripes" on each forewing. The outer edge of the forewing is black with a row of yellow spots. The veins are marked with black. The postmedian area of the hindwing is black with yellow spots along the margin. The inner margin of the hindwing has small red and blue spots. The ventral forewing margin has a yellow bar that is broken into spots. This broken bar is present in both sexes, and is used to distinguish P. glaucus from its close relatives.
Females are dimorphic. The yellow morph differs from the male in having a blue postmedian area on the dorsal hindwing. In the dark morph, the areas that are normally yellow are replaced with dark gray or black. The bluish postmedian area on the ventral hindwing has one row of orange spots.
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Eastern Tiger Swallowtail at Athens Botanical Garden.jpg|Eastern Tiger Swallowtail at the State Botanical Garden of Georgia
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Taxonomy
The first known drawing of a North American butterfly was of an eastern tiger swallowtail. It was drawn by John White in 1587, This species was later described by Carl Linnaeus in his 10th edition of Systema Naturae in 1758. In 2002, another closely related species, P. appalachiensis, was described by H. Pavulaan and D. M. Wright from the southern Appalachian Mountains. These two species can be separated from P. glaucus by size; P. canadensis is smaller and P. appalachiensis is larger. These two also have a solid yellow bar along the margin of the ventral forewing.
Similar species for the dark P. glaucus female include the pipevine swallowtail (Battus philenor), the spicebush swallowtail (Papilio troilus), and the female black swallowtail (Papilio polyxenes). B. philenor differs from the dark morph P. glaucus by the row of light-colored spots on each wing margin. P. troilus is more greenish, and has two rows of orange spots on the ventral hindwing. P. polyxenes is smaller, and the ventral hindwing has two rows of yellow-orange spots. although is rarer in southern Florida and absent from the Florida Keys.
P. glaucus can be found almost anywhere deciduous forests occur. Common habitats include woodlands, fields, rivers, creeks, roadsides, and gardens. It will stray into urban parks and city yards. Because it has adapted to many different habitats and host plants, P. glaucus is a generalist, and is not considered threatened. This is likely due to genetic traits and differential detoxification abilities. However, as compared to Papilio canadensis, at the northern overlap between the two species, P. glaucus survive very poorly through their first larval instar when settling on a quaking aspen (Populus tremeloides) tree and their survival rate under those conditions are approximately 15%, whereas P. canadensis thrives on this food plant. Males seek females by patrolling habitats containing the larval host plants. During courtship, the male and female fly about each other prior to landing and mating. The male releases perfume-like pheromones during courtship to entice the female into mating.
Adults use a wide range of food sources, most preferring to nectar on sturdy plants with red or pink flowers. Adults have also been seen feeding on dung, carrion, and urine. The egg is round and green, later turning yellowish green with reddish dots. It takes between 4 and 10 days to hatch.
Caterpillar
thumb|right|Fifth [[instar caterpillar, shortly before pupating]]
The caterpillar eats the leaves of the host plant. It will rest on a silk pad on a leaf, with the edges of the leaf folded over itself and held together with silk.
Defense against predators
thumb|Caterpillar with an everted [[osmeterium]]
The first three instars of the caterpillar are bird dropping mimics, coloration that helps protect it from predators. In later instars, the eyespots on the thorax serve to deter birds. Like all members of the family Papilionidae, the caterpillar of P. glaucus possesses an osmeterium, an orange, fleshy organ that emits foul-smelling terpenes to repel predators. Normally hidden, the osmeterium is located on the first segment of the thorax, and can be everted when the caterpillar feels threatened. The combination of eyespots and osmeterium makes the caterpillar resemble a snake.
Since adults are palatable, dark morph females use Batesian mimicry to protect themselves from vertebrate predators by mimicking the poisonous pipevine swallowtail. Dark morph females are more prevalent in the south, where B. philenor is more common.
See also
- Two-tailed swallowtail
- Western tiger swallowtail
- Canadian tiger swallowtail