The Giant Swallowtail flies with a graceful series of strong flaps and short glides, usually at about a human observer's eye level (Brock and Kaufman 2003).
The Giant Swallowtail (Papilio cresphontes) is a large, mainly blackish brown and yellow swallowtail with a spoon-shaped "tail" on each hind wing. The end of each tail has a yellow center. The Giant Swallowtail occurs in a wide range of natural and disturbed habitats. Its geographic range extends across most of the eastern United States and adjacent Canada and south through the Caribbean, Mexico, and Central America into South America. In the northern United States, it occurs only in scattered local colonies, but it is common to the south (Opler and Krizek 1984).
The Giant Swallowtail is found throughout most of the eastern Unites States and adjacent Canada south through the Caribbean, Mexico, Central America, and most of South America (Opler and Krizek 1984; Opler 1992; Brock and Kaufman 2003). In the northeastern United States and adjacent Canada, it occurs only in scattered local colonies, but it is common farther south (Opler and Krizek 1984). It has a more limited distribution in the southwestern U.S., but expanded into the Los Angeles basin during the last two decades of the 20th century (Brock and Kaufman 2003). It strays regularly to eastern Colorado and rarely to North Dakota and Wyoming (Opler 1999).
The Giant Swallowtail is found in a wide variety of natural and disturbed open habitats, including parks, suburbs, and citrus groves, as well as more natural areas (Cech and Tudor 2005). In the northern U.S., it is most often associated with rocky and sandy exposed hillsides near streams or gullies; in the southern U.S., it is often associated with pine flatwoods, towns, and citrus groves (Opler 1992).
Larvae of the Giant Swallowtail feed on a variety of plants in the Rutaceae (citrus family), including Wild Lime (Zanthoxylum fagara), Hercules Club (Zanthoxylum clavaherculis), Common Rue (Ruta graveolus), Torchwood (Amyris elemifera), cultivated citrus (Citrus spp.), Northern Prickly-Ash (Zanthoxylum americanum), and Hop Tree Wafer-Ash (Ptelea trifoliata) (Cech and Tudor 2005). In the northern U.S., the primary host is Northern Prickly-Ash (sometimes Hop Tree); in the southern U.S., the primary hosts are cultivated Citrus, Hercules Club, and Torchwood (Opler 1992).
Young Giant Swallowtail caterpillars rest on leaves, while later instars (developmental stages) rest on small branches. Most feeding occurs at night. Instars vary in appearance, but all show disruptive color patterns that make them resemble (to humans and very likely to birds as well) bird droppings (Opler and Krizek 1984).
The Giant Swallowtail somewhat resembles the very rare Schaus' Swallowtail (Papilio aristodemus ponceanus) of extreme southern Florida, but the larger Giant Swallowtail has yellow centers on its long hindwing tails (Schaus' has shorter, yellow-edged tails) and yellow bands on the forewing above that form an "X" near the wingtips (Brock and Kaufman 2003; Cech and Tudor 2005). These yellow forewing bands are noticeably broader in the Giant Swallowtail (Opler 1992). Below, Schaus' Swallowtail has a much larger rusty brown patch (Brock and Kaufman 2003; Cech and Tudor 2005). The sexes of Giant Swallowtail are similar, but male Schaus' Swallowtails have yellow antennal clubs (the females antennae are all dark).
The Thoas Swallowtail (Papilio thoas) is extremely similar to the Giant Swallowtail and cannot be reliably distinguished in the field. This species, whose larvae feed on Piper and a number of species in the citrus family (Rutaceae), is essentially Neotropical, but occurs rarely in extreme southern Texas and can stray north to Colorado and western Kansas. (Opler 1999; Brock and Kaufman 2003)
The Ornythion Swallowtail (Papilio ornythion), an essentially Central American citrus-feeding species that reaches extreme southern Texas (and occasionally strays to western Texas, southern New Mexico, and western Nebraska), lacks yellow in the tail centers and has yellow forewing bands that do not merge (Opler 1999). Habits and flight are similar to those of Giant Swallowtail (Brock and Kaufman 2003).
The Broad-banded Swallowtail (Papilio astyalus) is a citrus-feeding species ranging from Argentina to Mexico and rarely straying north to southern Arizona and southern Texas. Compared to the Giant Swallowtail, the male has a broader yellow forewing band, a small yellow spot in forewing cell, and narrow all-black tails. (Opler 1999)
Wingspan of the Giant Swallowtail is 102 to 154 mm (Opler 1992).
In the U.S., Giant Swallowtails have two broods per year in the north (May-June and July-early September), and at least two or three broods in the Deep South (Cech and Tudor 2005). Adults are flying year round in southern Florida, most of the year in the Deep South, and from spring to fall farther north (Brock and Kaufman 2003).
Larvae of the Giant Swallowtail often feed on the leaves of cultivated citrus trees and are thus viewed as minor pests by citrus growers (Opler and Ktizek 1984; Brock and Kaufman 2003).
The giant swallowtail (Papilio cresphontes) is the largest butterfly in North America.[2] It is abundant through many parts of eastern North America; populations from western North America and down into Panama are now (as of 2014) considered to belong to a different species, Papilio rumiko.[3] Though it is often valued in gardens for its striking appearance, its larval stage can be a serious pest to citrus farms, which has earned its caterpillars the names orange dog or orange puppy.[4] The giant swallowtail caterpillars possess remarkable camouflage from predators by closely resembling bird droppings. They use this, along with their osmeteria, to defend against predators such as wasps, flies, and vertebrates.[4][5]
The giant swallowtail is common across the United States, reaching as far north as southern New England and southern Canada. South of the United States, it is found in parts of Mexico and also found in Jamaica and Cuba. The species was historically considered to occur in the western United States and into South America,[4] but now those populations are treated as a separate species, Papilio rumiko, based largely on DNA evidence.[3]
In the United States, P. cresphontes mostly inhabit deciduous forest and citrus orchards. They are only capable of overwintering in Florida and the deep South.[2]
One of the giant swallowtail's most notable features is its size. Females have an average wingspan of 5.5 in (14 cm), and up to 6.9 in (18 cm), while males' average is 5.8 in (15 cm), and up to 7.4 in (19 cm).
The wings are black with a horizontal yellow line across the forewings, and a diagonal yellow line across the hindwing. The underside of the wings is yellow with accents of black. A small patch of red on the ventral wing (within the small blue band) allows for distinction from the similar-looking Schaus' swallowtail.[4]
As well as eating valuable citrus crops, larvae eat a wide variety of plants in the family Rutaceae (citrus plants), including different types of prickly ash. They also consume some exotic Rutaceae species that have been introduced to North America, such as gasplant and sapote.
In specific local subpopulations (studied in Wisconsin, Ohio, and Florida), it was found that giant swallowtail caterpillars do better on their local host plant than on other giant swallowtail host plants. The local host caused the larva to develop faster than other plants that were also edible to the larva. However, this feeding specialization hypothesis has not been tested in the species as a whole beyond these three regions.[5]
Nectar plants for adults include Lantana, Azaleas, Bougainvilla, Saponaria officinalis, Hesperis matronalis, Solidago, Lonicera japonica, and Asclepias incarnata.[4] Along with flower nectar, adults can also consume liquid from animal waste.[4]
Females lay eggs on the tops of the leaves of one of their preferred host plants. This is because the first larval instars are unable to move from plant to plant, so the mother must select an appropriate plant to support them. One egg is lain at a time, as opposed to in clutches. The small egg (1–1.5 mm) is brownish colored, but appears more orange due to a special orange colored secretion.[4]
Once emerged from the eggs, there are five larval instars, wherein the larva grow to about 2 inches before pupating. Larvae are mostly nocturnal, feeding at night. Their appearance changes slightly throughout the instars, with the younger ones having setae and the older instars lacking setae.[4] The caterpillars have remarkable camouflage patterns.[5]
Larvae must find a vertical plant, or sometimes a man-made object, to form their chrysalis on, and often they choose the host plant they already occupy.[4] They attach themselves to their substrate of choice and molt to reveal a brown, mottled chrysalis (resembling a bit of dead twig) in which they remain for approximately 10–12 days.
Males search for females along set flight paths and near host plants, and mate with females in the afternoon.[4][2] Male and female then copulate facing away from each other.[6]
Giant swallowtails are most vulnerable to parasites when they are in their chrysalis. Common parasites include flies and wasps such as Brachymeria robusta, Pteromalus cassotis, Pteromalus vanessae, and Lespesia rileyi.[4]
Larvae have many adaptations to protect themselves from predators.
The caterpillars' intricate coloring patterns are an effective camouflage and defense against both vertebrate and invertebrate predators and parasites. It is thought that the coloration was naturally selected for because of its imitation of bird and lizard droppings. The caterpillar mimics certain droppings based on its habitat and which instar it is.[5] The caterpillars' coloration, particularly the saddle pattern, is also thought to be disruptive coloration. This means the coloration makes it harder for a predator to distinguish the shape of the camouflaged prey, which explains the continuation of this coloration pattern in larger instars that are too large to be mistaken for bird droppings.[5] It has also been hypothesized that the older instars' pattern is meant to be reminiscent of a snake.[4]
When camouflage is not enough, larvae will employ their osmeteria when they are threatened. The osmeterium is an organ behind the head that “inflates” into an orange/red Y-shaped growth that resembles a snake's forked tongue. By the fourth instar, the osmeterium is more than just a startle mechanism and also has bad-smelling and toxic mixture of acidic chemicals. This is only effective on small invertebrate predators, and the caterpillar will try to rub its osmeterium on the predator to deter it.[4] It has been experimentally tested and found that osmeteria are ineffective at deterring predation from birds.[7]
Giant swallowtail butterflies must correctly identify their host plants by antennal sensitivity to the specific volatile compounds in the plants. A study found that antennal response to these volatiles depends upon the concentration of the volatiles, the host plant of origin (whether it is a primary or secondary host), and the sex of the butterfly. This last dependency is thought to be because the females, not the males, must identify the correct host plant for egg laying.[8]
Because of the butterfly's notably large wingspan (14 to 18 cm), giant swallowtails are very strong fliers and are able to glide long distances with very few wing beats.[4]
Sometimes referred to as "orange dogs", "orange pups", or "bird poop caterpillars"[9] by farmers, the larva targets all varieties of citrus plants, often causing significant damage to new foliage and younger trees, which they can more thoroughly defoliate. Large mature citrus trees are not generally significantly impacted. Outside of farms, the species is valued for its aesthetic appeal and can also be raised to butterflies successfully at home.
Biological insecticides, such as Bacillus thuringiensis, as well as chemical insecticides, are used to protect trees against larvae.[4] Methionine, an essential amino acid in humans, has also been found to be an effective killer of caterpillars, with possible use as a nontoxic pesticide against giant swallowtail larvae.[10]
There has been a northern expansion of the range of the giant swallowtail in recent years which has been linked to increasingly warm temperatures, and particularly to a lack of September frosts in regions of expansion starting in 2001. Larvae were then able to withstand a few frosts before they pupated. The immediate effects of this warming, as well as their effect on host plants and predators, can explain the giant swallowtail's range expansion.[11]
Egg
P. cresphontes caterpillar showing defensive posture
Adult, underside
In flight. Video clip
The giant swallowtail (Papilio cresphontes) is the largest butterfly in North America. It is abundant through many parts of eastern North America; populations from western North America and down into Panama are now (as of 2014) considered to belong to a different species, Papilio rumiko. Though it is often valued in gardens for its striking appearance, its larval stage can be a serious pest to citrus farms, which has earned its caterpillars the names orange dog or orange puppy. The giant swallowtail caterpillars possess remarkable camouflage from predators by closely resembling bird droppings. They use this, along with their osmeteria, to defend against predators such as wasps, flies, and vertebrates.
