Luna moths are a striking lime green in color, with handsome eyespots on their wings. With a wingspan of up to 4 ½ inches, they are among the largest moths in North America. And the adult moths live for just seven days, in which all they do is reproduce as much as possible before they die.
This brief lifespan and their nocturnal habits make the luna moth rare and exciting to see, even though they are large in number and common in the regions where they live and breed. Many people are eager to learn more about the elusive actias luna, the American Moon Month.
Where do Luna Moths Live
Luna moths are native to North America, where they can be found east of the Great Plains, but as far west as Saskatchewan, Canada. They range from the south of Canada to the north of Mexico, although they have been seen as far south as Mexico City. The population is greatest in the states of Tennessee, Georgia, the Carolinas, and Alabama.
They live in deciduous forests, where the luna moth caterpillar feeds on the leaves of trees.
In the northern parts of their range, they produce only once a year, so adult luna moths are only to be seen for a few short nights in the mid-summer, from June through July. They are largest in the north, and have the most vivid green color.
In the southern part of their range, they can reproduce up to three times a year, emerging in springtime and having two or three generations of Luna Moths in a single year. In the southern part of their range, they tend to be smaller and have wings that are a paler, yellow-green in color.
The Luna Moth Life Cycle
Like all moths, luna moths lay eggs on the leaves of trees on which the caterpillars will feed. A female luna moth will lay 400-600 eggs during her short life, in small clutches of 4-6 eggs at a time. The eggs incubate for 1-2 weeks and then hatch into caterpillars. The caterpillars feed voraciously for up to two months, before making a cocoon and pupating.
About Luna Moth Caterpillars
While adult luna moths are rare and impressive, luna moth caterpillars are also exceptional little creatures, worth paying attention to themselves.
Luna moth caterpillars eat the leaves of deciduous trees in the region where they live. Luna moth caterpillars can eat the leaves of a wide variety of trees, including:
However, the caterpillars of one region or habitat will not always live and thrive on the leaves of the tree of another region, even though Luna Moth caterpillars local to that tree species will. Northern luna moth caterpillars frequently live on white birch, while their southern cousins often eat hickory, walnut, or sumac leaves. Hickory and sweetgum appear to be good luna moth caterpillar food sources for all regions.
When growing luna moth caterpillars in captivity, hickory is a difficult food source because the branches wilt quickly when cut. It’s best to have a large supply of living hickory trees in order to have enough to feed hungry caterpillars. This is why most people choose to feed sweetgum to luna moth caterpillars when growing them in captivity. However, when grown in captivity, it is good to provide the young caterpillars with a variety of different tree species to see which they prefer. Just make sure that you offer a species of tree that is plentiful enough to keep up with their enormous appetites.
While they are young, luna moth caterpillars will often stay close to each other, and will sample several kinds of trees. Over time they will move on to a solitary life, feeding on the tree leaves of whatever tree species they have come to prefer. When they get larger, they can strip a whole branch of leaves in a day, due to their voracious appetites, so they require substantial room to forage in the wild. However, the overall population of Luna Moths is small enough that they don’t pose any threat to forests or host trees.
Like many insects, the luna moth caterpillar goes through several distinct growth phases. These phases are called instars. At every instar, the caterpillar will shed its skin and emerge larger and with an altered appearance. Luna moth caterpillars go through five instars.
- The first instar: The caterpillar emerges from the egg a pale green color, often with even paler green spots, covered with small spines. It is typically 6-8 millimeters long
- The second instar: The caterpillar develops yellow or golden spots, and spines are fewer but thicker. It is typically 9-10 millimeters long
- The third instar: The third instar of the luna moth caterpillar has the same lime green color, but the yellow spots tend toward deeper gold or orange, and spines are even shorter and thicker. It is generally 13-15 millimeters long at this phase
- The fourth instar: During the fourth instar, the spot pattern changes, and deep ridges have developed on the caterpillar. Spines are fewer, longer, and thicker. It has begun to take on a rough surface texture. During this phase, it grows to 23 millimeters long.
- The fifth instar: During the fifth and final instar, the caterpillar has a rough surface texture with very few spines. It is lime green with small orange and yellow spots. It grows to an enormous 65 millimeters long.
When the caterpillar is ready to pupate, it loses its bright green color and turns a deep rusty orange color.
How they defend themselves
Luna moth caterpillars are so large that they are an attractive meal for a wide variety of predators. They rely on a variety of methods to defend themselves.
- Camouflage: The bright green color of the luna moth caterpillar is similar to the colors of the leaves it lives on and eats. It can be difficult for predators to see.
- Behavior: When threatened, the luna moth caterpillar raises the front part of their body and retracts their head into an odd “sphinxlike” pose, perhaps intended to make them look less like a caterpillar. They can also make a clicking noise with their mandibles.
- Attack: When under attack, luna moth caterpillars regurgitate unpleasant fluids onto their attacker. This fluid has been shown to deter predation from ants and mice.
Luna Moth Caterpillar Pupae
When the luna moth larvae are large enough, they begin to make a cocoon. The cocoon is a single layer of silk, and often incorporates leaves into the wrapping. While some moths anchor their cocoons to a tree branch, but Luna Moths do not, so the cocoons often fall to the ground.
In the northern part of their range, where luna moth only reproduce once a year, the moth may remain inside the cocoon all winter long, entering a state called diapause. Diapause is similar to hibernation, and the moth will remain inside the cocoon until the exterior light and temperature levels are favorable enough to trigger it to emerge.
In warmer southern climates, the luna moth may reproduce up to three times a year, so the larvae only remain inside the cocoon for a couple of weeks before emerging as adults.
Luna moths are a particularly active species inside their cocoons. When disturbed or threatened, they will actively wiggle and produce sounds.
It is in the pupa stage inside the cocoon that it first becomes possible to differentiate male and female luna moths. Female luna moths develop two distinct longitudinal creases or notches in the fourth and fifth segments of their abdomen. Males do not have these creases.
Adult Luna Moths
When they emerge from their cocoons, luna moths are their most vulnerable. Their wings are wrinkled and compressed against their bodies, and it will be a few hours before they have sufficient strength to fly. The males emerge from their cocoons a few hours before females, and they hang under a leaf, slowly pumping fluid from their abdomens out to expand and strengthen their wings enough for flight at night.
When female luna moths emerge, they also need to dry and strengthen their wings. But, unlike males, they do not take flight once their wings are dry and ready. Instead, they begin to emit pheromones to attract males. Female luna moth pheromone production peaks at about midnight, when the males are most active.
Male luna moths have large, sensitive antennae designed to detect the hormonal signals from the female. These antennae are the primary way to distinguish male and female adult luna moths, and the male can detect female pheromones over very long distances. Once the male has located a female, he mates with her and then flies off to find another female. Mating peaks within an hour or two of midnight, and the male will continue to mate as long as he is able.
Adult luna moths do not eat. In fact, they do not even have functional mouths. In the northern climates where luna moths only emerge and breed annually, the adults are living on the fat stores accumulated as a caterpillar in the summer of the year before. The adults will only live as long as that stored energy is able to sustain them, just the 5-7 days long enough to reproduce.
When a female luna moth has mated, the following evening, she will begin laying her eggs. She flies from tree to tree, laying small clutches of 4-7 eggs at a time. Over the next few days, she will lay up to 600 eggs in this way, before she, too, will exhaust her resources and die.
A week or two later, caterpillars emerge from the eggs and the cycle begins again.
Why do People Love Luna Moths
People have an enduring affection and interest in luna moths. It’s not just because they are so large and so beautiful, although that’s certainly part of the attraction. It’s also because their lives are so short, and their habits so nocturnal, that, even though they are large in number, they are rarely seen. Even in optimal conditions, to see a luna moth in the wild means that you are in the south eastern United States where they reproduce more than once a year, giving you two or three weeks in a summer where you might see a moth, instead of just one. Because they are most active in the few hours after midnight, and live for such a short time, many people are excited to just see them at all.
This fascination and elusiveness in the adult moth is the primary reason that many people choose to grow luna moth caterpillars in captivity. They are inexpensive fairly easy to raise, and it guarantees a chance to see and experience the incredible American Moon Moth up close.
Some people even omit the caterpillar phase, and simply purchase luna moth pupae. Because the adults do not eat, they are easy to care for, and only need suitable breeding habitat. However, to protect the natural environment, the USDA only allows luna moth to be sold, shipped, and raised in states where they naturally occur. Residents of western states need to apply for a permit from the USDA/APHIS to purchase and grow luna moths. Application for a permit is free, and generally approved, provided the moths are being kept and grown for educational purposes.
The strikingly beautiful and fleeting luna moth will continue to excite, intrigue, and enchant people for generations to come, thanks to their unique appearance and brief life span. It’s a wonderful and mysterious part of nature that people are happy to experience for themselves.