MANAGE FORESTS & LAND

  • FOREST HEALTH: LUNA MOTH

    The butterflies and moths are probably the most attractive and best known group of insects. Many of us are familiar with some of the large and showy moths and butterflies that grace the forests of East Texas. However, the caterpillars that eventually develop into these beautiful adult insects are not nearly as well known. Here we will consider the caterpillar (larva) and the adult (moth) of the luna moth (Actias luna). The luna moth is one of the most beautiful silk moths found in North America. The caterpillar or larva of the luna moth does not have a common name. When full grown, this caterpillar reaches a length of about three inches, is as big around as an adult’s index finger, and is harmless to people. The caterpillar is a lush green color and covered with numerous short, stout hairs. The segment just behind the head is rimmed with yellow and there is a conspicuous yellow band across the top of every abdominal segment. Several conspicuous bright red spots are present on each body segment. A row of spiracles (where the caterpillar breathes) occurs along both sides of the body. Each spiracle appears as a pink spot surrounded by yellow, and there is a distinct yellow line running along each side of the body just below the spiracles. The thoracic legs (the true legs just behind the head) are yellow and black. The fleshy prolegs (false legs that are lost before the insect becomes an adult) are green and yellow and black. In summary, the caterpillar of the luna moth is very colorful.

    Luna Moth in Larva Stage

    The caterpillar feeds on a wide variety of trees including hickory, persimmon, sweetgum, oak, and willow. In spite of the fact that this large caterpillar can consume a considerable amount of foliage, it doesn’t cause any significant damage. In East Texas there may be up to three generations each year which means the caterpillar could be present throughout the warmer months. The luna moth is a member of the family of moths known as silk moths. When the caterpillar is fully developed, it begins a marvelous process -- the transformation to a pupa. To do this, it crawls to the ground and begins to weave a silk cocoon around itself. In the process of forming the cocoon, the caterpillar finds a dry leaf and carefully weaves the leaf into the silk. The leaf hides most of the cocoon making it difficult to see among other leaves and debris on the ground. The pupa will remain protected in the cocoon through the winter and the adult moth likely will emerge the next spring.

    The adult stage, most commonly found in April and May, is the spectacular pale green luna moth and has a wingspan of about four inches. This moth is best known for the long, curved tails on its hind wings. The top edge of each front wing is bordered with a purple-brown band. Each wing has a clear eye spot bordered with black and yellow. The moth’s body appears to be covered with white cotton. The female is slightly larger than the male and both sexes have the same color pattern. The male and female moths can be identified by carefully observing the antennae. They both have antennae that resemble feathers, but the male’s antennae are much fuller than the female’s. There is an important reason for the male’s large antennae -- finding a mate. The male luna moth finds his mate by being attracted to an odor (called a pheromone) produced by the female moth. The male is able to smell the female’s scent through his antennae. An unmated female moth placed outdoors in a screen or cloth cage may attract several male moths. It makes for an interesting experiment.

    Luna Moth

    Both sexes are attracted to lights at night and that is a good place to look for them. Lights having a bluish tint (for example mercury vapor lamps that are commonly used for street lights and guard lights) are attractive to many insects, including the luna moth. Unfortunately sodium vapor lamps, which have a distinct yellow color, are replacing mercury vapor lamps. Yellow and red colors attract very few insects. Red porch lights are not a common sight, but yellow porch lights are frequently used because they are not attractive to insects.

    If one should happen to find a luna moth caterpillar, it is not difficult to rear it to the moth stage. If a caterpillar is found still feeding on the host plant, place the caterpillar, along with some host plant foliage, in a large container (one to two gallon size). Each day, fresh foliage should be provided for the caterpillar. It would be good to place two or three inches of loose leaf litter in the bottom of the container so the caterpillar will have a suitable place to pupate when the time comes. If the caterpillar is found on the ground, chances are it has completed feeding and is searching for a place to pupate. In this case, place the caterpillar in a container with leaves (as described above) and before long it will probably change to a pupa. If kept indoors, a beautiful luna moth may emerge during the winter. Sometimes the luna moth caterpillar will be attacked by a parasitic wasp or fly. Since the larva of the wasp or fly usually feeds inside the body of the caterpillar, it may not be obvious that the caterpillar has been parasitized. A parasitized caterpillar may pupate, but rarely survives to become an adult moth.

    Luna Moth with full wing view.

    The luna moth is one of several large, beautiful moths commonly found in April and May in East Texas. Look for them around lights at night.
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