Luna Moth (Actias luna): Facts, Life Cycle and Wings

What does a luna moth look like?

A luna moth has lime-green to bluish-green wings and a fluffy white body. The front edge of each forewing is a thick band of maroon to purplish brown, and every wing carries an eyespot: oval on the forewings, round on the hindwings. The eyespots have rings of yellow, black, blue or reddish color and are thought to startle or distract predators.

The most striking feature is the pair of long tails trailing from the hindwings, often slightly twisted. At rest, with the wings spread or tented over the body, the moth can look remarkably like a cluster of fresh green leaves.

Males and females are similar in size and color. Males have broad, feathery antennae used to detect the scent of females, while females have narrower antennae and a plumper abdomen that holds 200–400 eggs. Color also varies by season and region: spring and northern moths tend to be bluish green, while summer generations in the south are often more yellowish green.

How big is a luna moth?

The luna moth is one of the largest moths in North America. Its wingspan is usually 8–11.5 cm (3.1–4.5 in), and exceptional specimens with wider wings have been reported. Including the tails, a luna moth can measure well over 10 cm (4 in) from head to tail tip.

Large as it is, the luna moth is small next to the tropical giants. The Atlas moth of Asia has a wingspan of about 25 cm (10 in). For the full ranking, see what is the largest moth in the world? and the Atlas moth profile.

Habitat and range

Luna moths live in deciduous and mixed hardwood forests across eastern North America. In Canada they range from Saskatchewan east through Ontario and southern Quebec to Nova Scotia. In the United States they occur in almost every state east of the Great Plains, from Maine to Florida and west to eastern Texas, with records reaching northern Mexico.

They need trees that their caterpillars can eat, so they are found in woodlands, forest edges, river valleys and leafy suburbs with mature trees. Adults are often discovered in the morning resting on a wall, window or tree trunk near a light that attracted them during the night.

The luna moth is the only member of its genus in North America. Its closest relatives are the other “moon moths” of the genus Actias in Asia and Europe, such as the Indian moon moth (Actias selene) and the Spanish moon moth (Graellsia isabellae, sometimes placed in Actias). In its own forests it shares the night with other giant silk moths, including the brown polyphemus moth and the cecropia moth, North America’s largest native moth. None of them has the luna moth’s green wings and long tails, so it is hard to mistake.

What do luna moths eat?

Only the caterpillars eat. They feed on the leaves of broadleaf trees, especially walnut, hickory, sweetgum, white (paper) birch, persimmon and sumac. Preferences differ by region: northern caterpillars tend to rely on birch, while southern ones often use sweetgum, hickory and walnut.

Walnut and hickory leaves contain juglone, a chemical that deters or poisons many insects. Luna moth caterpillars produce high levels of digestive enzymes that help neutralize it, which lets them use trees that other caterpillars avoid. They rarely become numerous enough to damage their host trees.

Adult luna moths do not eat or drink at all. Like other giant silk moths, they have only vestigial (tiny, non-functional) mouthparts and live on the fat built up by the caterpillar. The reasons are explained in why do luna moths have no mouth?

Life cycle

The luna moth goes through complete metamorphosis: egg, caterpillar (larva), pupa and winged adult.

• Eggs: A female lays her eggs singly or in small groups on the undersides of leaves of a suitable tree, over several nights. The eggs hatch in about one to two weeks.
• Caterpillar: The caterpillar molts four times, passing through five stages called instars. It is green throughout, with short bristles and small yellow or magenta dots along its sides. Growth takes roughly six to seven weeks in the north and less in warm regions.
• Cocoon and pupa: The full-grown caterpillar empties its gut, climbs down to the ground and spins a thin, single-layered silk cocoon wrapped in dead leaves. Summer pupae develop in about two to three weeks. In fall, the pupa enters diapause, a dormant state, and spends the winter in the leaf litter, a pupal stage of up to nine months.
• Adult: The moth breaks out with soft, crumpled wings and pumps hemolymph (insect blood) into them. Within two to three hours the wings have expanded and hardened, and it can fly.

The number of generations depends on climate. In Canada and the northern United States there is one generation a year, with adults flying mainly in late May and June. Around the mid-Atlantic states there are two, often in April and July, and in the far south three generations can fly from as early as March.

Behavior: night flights, scent and courtship

Luna moths are strictly nocturnal. By day they rest motionless among leaves or on bark, where their green color is good camouflage.

Courtship is driven by scent. After dark, a newly emerged female sits on a tree and releases a pheromone, a chemical signal. Males follow the scent upwind with their feathery antennae, and giant silk moth males can track it over long distances. The luna moth’s main pheromone component has been identified as a species-specific aldehyde that attracts no other moth species in field tests.

Mating usually begins after midnight. If undisturbed, the pair can stay coupled until the following evening. The female then spends her remaining nights laying eggs, and both sexes die within about a week of emerging.

How do luna moth tails fool bats?

Bats are major predators of night-flying moths, and luna moths have no ears to hear their sonar. The long hindwing tails are their answer. As the moth flies, the tails twist and spin, producing extra sonar echoes that draw a bat’s attack away from the body.

In experiments published in 2015, big brown bats hunted luna moths with intact tails and moths whose tails had been cut off. Bats caught about 35% of intact moths but about 81% of tailless ones, and in more than half of attacks on tailed moths the bat aimed at the tails. A missing tail is a small loss for a moth that only needs a few nights of flight. Studies of the moth family suggest that long tails evolved several times among giant silk moths, probably for this reason.

Predators and threats

Bats hunt the adults at night, and birds and other insect-eaters take both adults and caterpillars. The caterpillars are not chemically defended, but they have their own tricks: when attacked, they make audible clicking sounds with their jaws and then regurgitate gut fluid, which has been shown to deter several predators.

Parasitoids, insects whose larvae develop inside a host, kill many caterpillars. One of them, the tachinid fly Compsilura concinnata, was brought from Europe to North America for most of the 20th century to control the invasive spongy moth (formerly called gypsy moth). It also attacks luna moth caterpillars and other native silk moths, and researchers consider it a cause of collateral damage to their populations.

Other pressures include the loss of forests, pesticide spraying and artificial light at night, which can pull moths away from their habitat and disrupt mating. Wild silk moths are reported to have declined in parts of their range since the 1960s. You can read more about lights in why are moths attracted to light?

Conservation status

The luna moth has not been assessed by the IUCN Red List. NatureServe ranks it as globally secure (G5), and it is not listed under the US Endangered Species Act or by CITES. It remains widespread and fairly common across its range, even if local populations may fluctuate. For where and when to look for one, see are luna moths rare?

Luna moths and people

The luna moth was the first North American giant silk moth described in the scientific literature: the English naturalist James Petiver wrote about it in 1700. Carl Linnaeus gave it its scientific name in 1758, after Luna, the Roman goddess of the moon.

Its beauty has made it a favorite of naturalists and schools, where it is often used to teach insect life cycles. In 1987 it appeared on a United States first-class postage stamp, at the time the only moth on a US stamp. Luna moths are completely harmless to people and do no damage to gardens or trees, so the best way to enjoy one is to look, take a photo and leave it where it is.