The Giant Swallowtail Butterfly
by George Giltner
The giant swallowtail is common among zinnias, pentas, milkweeds, azalea, Japanese honeysuckle, goldenrod, and many other flowers. The adults are easily identified with their large black wings crossed by a striking thunderbird display of yellow dot bars. The underside of the wings is primarily yellow. The total wingspan averages around 5.7 inches. These butterflies make excellent views in a red background of “Amazon Pentas”. As the dew begins to evaporate, they spread their large wings flat while dipping into the nectar of colorful flowers.
The caterpillars can be found on citrus where they can be a pest on young plants. However on mature citrus, their defoliation causes little damage. The orange or cream eggs are found singly on the upper surface of leaves. After hatching, the larvae feed mainly during the night. Their cryptic coloration of bird droppings is very effective against predators. When attacked, the caterpillar projects a “Y” shaped gland that emits a pungent odor (vomit) of butyric acids that is toxic to predators like ants and spiders. Also birds are repelled by internal chemicals of the larvae. Older larvae instars resemble small stubby snakes; therefore they are typically named “orange dogs”.
Image 1. The “orange dog” caterpillar feeds on citrus but becomes a swallow tail butterfly. It tends to look like bird droppings.
The weak point in the life cycle of the giant swallowtail is the pupae. It is parasitized by a tachinid fly, a chalcidid wasp, two pteromalid wasps, and other beneficial insects. The brownish chrysalis is attached at a 45 degree angle to objects with a silken pad on one end and a silk thread at the other. Two to three generations occur each year in Louisiana.
The best way to control the caterpillars on small citrus is to move them to larger citrus. Then you can enjoy giant swallowtail butterflies on the flowers and have little damage to the citrus. Large infestations of larvae can be controlled with “Bt”, the active ingredient in products like Dipel and Thuricide, both organic pesticides. But who would want to destroy such a beautiful insect?
Image 2. An adult swallowtail butterfly doing its pollination work.