Spicebush Swallowtail

Naming

The spicebush swallowtail derives its name from its most common host plant, the spicebush, members of the genus "Lindera".

Behavior

When female swallowtails decide which leaf to oviposit on, they frequently will drum their forelegs toward a leaf to identify it. Their forelegs have chemoreceptors located in the foretarsi that assess the chemical makeup of the leaf and use that information to decide if it is an acceptable spot. In general, females have shorter and denser sensilla on their forelegs than males, which may be a result of their having to sustain frequent heavy strokes.

The eggs of the Spicebush Swallowtail are greenish-white in color, are fairly large and are laid one or two at a time on a spicebush leaf. Once hatched, the young larvae chew through the leaf from the edge to the midrib, about 3/4 of an inch form the tip of the leaf. The larva lies on the midrib and exudes silk. Upon drying, the silk contracts and causes the leaf to fold up around the larva to form a shelter. At first, young larvae are brownish in color. The brown color of the larvae is independent of leaf color and will occur even on a green leaf. A folded leaf serves as the home for the young larvae. During the day, the larvae remain in the shelter so as to avoid predators and come out at night to feed. Additionally, if larvae are disturbed while rolled up in the leaf, they emit a foul-smelling substance.

When these larvae reach later stages, they turn greenish-yellow before pupating. Older larvae live in a leaf, rolled-up and lined with silk and held together by a line of silk. In order to pupate, the larvae will leave the shelter and find the underside of a leaf near the ground to do so. Upon discovery of a suitable leaf, the larvae begin the pupating process by emitting silk from their salivary glands, which helps attach the larvae to the branch or leaf. Then the larvae turn around while still emitting silk, which creates a "safety harness" for the pupating process. At the end of the pupating process, the larvae have become pupae which are either brown or green.

The practice of turning either brown in winter or green in summer is called seasonal polyphenism. Because the color of the pupa reflects the color of the deciduous host plants, since the leaves will turn brown in winter and green in summer. Even in cases where the leaves are not yet brown, the pupa appear to turn that color in anticipation of the changing colors.

Roughly three generations of Spicebush Swallowtails occur each year. Most develop into adults throughout the range between the months of February and November. The entire development process from egg to adult takes about a month. Once they have reached the adult stage, "Papilio troilus" can live anywhere from two days to two weeks dependent on resource availability and predator avoidance.Spicebush Swallowtails are able to thermoregulate their thoraxes better than other "Papilio" species, perhaps due to their darker body and wing color. This allows them to fly and feed at lower temperatures than their counterparts.Spicebush Swallowtails often engage in "puddling," a type of behavior which occurs while adults are flying in search of food or mates. "Puddling" reflects the fact that while engaging in either feeding or mating behavior; i.e., when they are away from home; Spicebush Swallowtails tend to stay in groups. These groupings are typically located on the banks of water, such as sandy or moist ridges. When "puddling" in these groups, the "Papilio troilus" will extract moisture from the soil or sand near the water.In general, both sexes will copulate with several different mates during mating season. However, each time a female mates, she becomes less likely to mate again.

One key known form of communication among Spicebush Swallowtails occurs during mating. Visual cues are important for males to find females, and courtship displays can be elaborate. While these courtship displays occur, the female and male are often in contact, which is likely a way for them to relay information to one another. Additionally, the male butterfly will typically emit pheromones around the female butterfly and the female will use their scent to make her decision about mating.

Females can often be found outside the treeline, in areas of direct sun. This may be due to the fact that these areas are in direct sunlight, which allows for higher thoracic temperatures. Males are less concerned with direct sunlight during mating because their thoracic temperature rises while performing vigorous courtship dances. Males may perform these courtship dances both to females perched on host plants as well as those flying freely.

Habitat

The host plants of the Spicebush Swallowtail are most commonly either spicebush or sassafras. Other possible host plants include Sweet bay and Prickly Ash, as well as tulip tree, sweetbay, camphor and redbay. Redbay and Swampbay are the primary host plants for members of the "Papilio troilus ilioneus" strain, while spicebush and sassafras as the primary hosts for "Papilio troilus troilus". However, when given the choice between spicebush and sassafras, the "P. troilus troilus" showed no significant preference for either.

Additionally, "P. troilus ilioneus" live only on redbay because that is the primary host plant within the Southern range. However, in a test of "P. troilus troilus" and P". troilus ilioneus" on redbay, sassafras and spicebush, although the "P. troilus ilioneus" had higher growth and survival rates on redbay than the "P. troilus troilus", as a holistic group, both subspecies performed better on sassafras or spicebush over time.

In general, Spicebush Swallowtails tend to stick to plants that are members of the family "Lauraceae". The preference for "Lauraceae" is so consistent among Spicebush Swallowtails that under experimental conditions, when placed in an environment with leaves other than "Lauraceae", "P. troilus" died without eating anything. This fact is especially noteworthy because "Lauraceae" are distantly related to the host plants of other species that are food for "Papilio" caterpillars. The fact that spicebush swallowtails live and feed primarily on "Lauraceae" only is noteworthy also because most other varieties of swallowtail butterflies are nowhere near as specific. Part of the reason for the selective nature of "P. troilus" and host plants may have to do with the requirement of positive stimuli to confirm that a plant is "Lauraceae" among "P. troilus" before they will feed on it, while "P. glaucus", for example, will at once try to feed on any plant presented to it.

The insistence on feeding primarily on "Lauraceae" has its advantages for Spicebush Swallowtails. They are able to feed 2-4 times more adeptly and efficiently on "Lauraceae" than "P. glaucus" on the same plant, for example, who feed on "Lauraceae" as well as other types of plants. In addition, there has not been any other Lepidoptera species which feeds as efficiently as the "P. troilus" on spicebush.
However, none of the host plants of "Papilio troilus" occur throughout the full range of the Spicebush Swallowtail. As stated above, the "P. troilus ilioneus" strain, found in Florida, mostly feeds on redbay, while "P. troilus troilus" feeds on either sassafras or spicebush. In a study, it was found that those spicebush swallowtails that normally feed on redbay did not grow as well on spicebush or sassafras during the first instar of development, while all insects studied grew better throughout the larval period on sassafras or spicebush. In addition, the "ilioneus" strain was typically larger in size than the "troilus".

In a recent study, 3-"trans"-Caffeoyl-muco-quinic acid was found to be the substance that compelled Spicebush Swallowtails to lay their eggs on members of "Lauraceae". However, 3-"trans"-Caffeoyl-muco-quinic acid is a component of the extract from sassafras plants but not from spicebush, redbay or camphortree, the other top three host plants of Spicebush Swallowtails. This substance is not necessarily itself the stimulant but instead activates another as yet unknown compound that thus compels the Spicebush Swallowtail to lay eggs. Thus, this substance may hold the link for why some Spicebush Swallowtails prefer to lay eggs on sassafras rather than spicebush. In addition, 3-"trans"-Caffeoyl-muco-quinic acid is a member of a family of acids, hydroxycinnamic acids, which are present in oviposition stimulants for some members of all five families of swallowtail butterflies. Hydroxycinnamic acids are also present in the extracts from host plants for two other species within the genus "Papilio": the black swallowtail butterly, "P. polyxenes", and "P. protenor". Thus, hydroxycinnamic acids may help explain why many types of swallowtails choose to oviposit on the plants that they choose.

Reproduction

As larvae, Spicebush Swallowtails have two stages of mimicry. While the larvae are in the early stages, they are dark brown in color and thus appear to resemble bird droppings, which encourages predators to leave them alone. When the larvae have progressed to their fourth and last instar and are nearly ready to pupate, they turn a yellow-green color and are marked by two large black dots with a white highlight. The placement of these dots on the swollen thorax creates the illusion that the caterpillars are common green snakes. Mimicking snakes help the caterpillars to ward off predators, specifically birds. The caterpillar Spicebush Swallowtails enhance the physical resemblance behaviorally, as they have been observed to "rear up and retract the actual caterpillar head."

The osmeterium of the caterpillar also helps to enhance the resemblance to a snake. When attacked, the larvae will expose the osmeterium, a y-shaped organ typically folded up within the caterpillar. For many Spicebush Swallowtails, the osmeterium is red in color, thus creating the illusion of a snake tongue and even further enhancing the disguise.

Food

Spicebush Swallowtail gain sustenance from eight major sources here are some examples: eating the leaves of host plant as larvae and drinking nectar as adults. Joe-pye weed, jewelweed and honeysuckle are favorite sources of nectar for the adults. They have also been known to drink nectar from Lantana, as well as thistles, milkweed, azalea, dogbane, mimosa and sweet pepperbush.Spicebush Swallowtails are able to thermoregulate their thoraxes better than other "Papilio" species, perhaps due to their darker body and wing color. This allows them to fly and feed at lower temperatures than their counterparts.

Predators

Many creatures are predators of the Spicebush Swallowtail. These species include birds, spiders, robber flies and dragonflies. All of these creatures will try to eat both adult Spicebush Swallowtail butterflies and youthful larvae.