thumb|Mounted specimen

The luna moth (Actias luna), also called the American moon moth, is a Nearctic moth in the family Saturniidae, subfamily Saturniinae, a group commonly named the giant silk moths.

The moth has lime-green wings and a white body. Its caterpillars are also green. Its typical wingspan is roughly , but wingspans can exceed , ranking the species as one of the larger moths found in North America.

Across Canada, it has one generation per year, with the winged adults appearing in late May or early June, whereas farther south it will have two or even three generations per year, the first appearance as early as March in southern parts of the United States. The initial Latin name, which roughly translates to "brilliant, feather tail", was replaced when Carl Linnaeus described the species in 1758 in the tenth edition of Systema Naturae, and renamed it Phalaena luna, later Actias luna, with luna derived from Luna, the Roman moon goddess. The common name became "Luna moth".

Distribution

The Luna moth is found in North America, from east of the Great Plains in the United States – Florida to Maine, and from Saskatchewan eastward through central Quebec to Nova Scotia in Canada. Luna moths are also rarely found in Western Europe as vagrants.

Life cycle

alt=Drawing of lifecycle|left|thumb|upright|Illustration by [[Edna Libby Beutenmüller|Edna Libby Beutenmuller from Field Book of Insects (1918)]]

Based on the climate in which they live, Luna moths produce different numbers of generations per year. In Canada and northern regions of the United States, they are univoltine, meaning one generation per year. Life stages are approximately 10 days as eggs, 6–7 weeks as larvae, 2–3 weeks as pupae, finishing with one week as winged adults appearing in late May or early June. In the mid-Atlantic states, the species is bivoltine, characterized by two generations per year. In contrast, farther south, they are trivoltine, producing three generations within the same time frame. In the central states, the first generation appears in April, the second in July. Even farther south, the first generation appears as early as March, with the second and third spaced eight to ten weeks later. This is a tree-dwelling species. Larvae stay on the same tree where they hatched until it is time to descend to the ground to make a cocoon. When females emerge from cocoons, they fly to preferred tree species, emit pheromones, and wait there for males to find them.

Pupae

The Luna moth pupates after spinning a silk cocoon, which is thin and single layered. Shortly before pupation, the final, fifth-instar caterpillar will engage in a "gut dump" where any excess water and intestinal contents are expelled. As pupae, this species is more physically active than most moths. When disturbed, the moths will wiggle within their pupal cases, producing a noise. Pupation takes approximately two weeks unless the individual is in diapause over winter, in which case the pupal stage takes about nine months. The mechanisms triggering diapause are generally a mixture of genetic triggers, duration of sunlight and temperature. The pupae have chitinous spurs near the base of the forewings. By vigorously moving about within the cocoon, these spurs tear a circular opening from which the imago emerges, the silk of the cocoon having also been weakened by the secretion of cocoonase, a protein-digesting enzyme.

Imago (winged)

Pupae transition to winged state after receiving external signals in the form of temperature change. When the adult Luna moths emerge from their pupae, their abdomens are swollen and their wings are small, soft and wet. The first few hours of adult life will be spent pumping hemolymph (invertebrates' equivalent to blood) from the abdomen into the wings. The moths must wait for the wings to dry and harden before being able to fly. This process can take 2–3 hours to complete. Luna moths are not rare, but are rarely seen due to their very brief (7–10 day) adult lives and nocturnal flying time. As with all giant silk moths, the adults only have vestigial mouthparts and no digestive system and therefore do not eat in their adult form. Instead, they rely on energy stored during their caterpillar stage. In regions where there are two or three generations per year, the second and third may have wing coloration that is more of a yellow-green compared to the first generation of the year.

<gallery>

File:Actias luna eggs sjh.JPG|Eggs from female raised in captivity, laid on coarse paper

File:Actias luna 1st instar hatching sjh.jpg|Hatching larva

File:Actias luna 4th instar sjh.JPG|4th-instar larva. Spots can also be yellow or magenta.

File:Actias luna spinning sjh.JPG|5th-instar larva starting to create a cocoon (note silk strands to leaves)

File:Actias luna male pupa sjh.JPG|Pupa, removed from cocoon. Eyes visible at head end (left)

File:Actias luna emergence male 7 sjh.JPG|Wings drying and enlarging after emergence from pupa

File:Actias luna mating sjh.JPG|Mating imagoes (winged adults). Male, with larger antennae, on left

</gallery>

Close-up images

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File:Luna Moth, closeup of antennae.jpg|Antennae (male)

File:Actias luna eyespot sjh.JPG|Eye-spot on hindwing

File:Luna moth eye spot.jpg|Eye-spot on forewing

File:Luna moth scales.jpg|Extreme close-up of scales in eye-spot

</gallery>

Predators and parasites

Some species of giant silk moth larvae are known to make clicking noises when attacked by rubbing their serrated mandibles together and can release a regurgitation of distasteful fluids. These clicks are audible to humans and extend into ultrasound frequencies audible to predators. Clicks are thought to be a form of aposematic warning signaling, made prior to predator-deterring regurgitation of intestinal contents. Luna moth larvae click and regurgitate, with the regurgitated material confirmed as being a predator deterrent against several species.

Imagos (winged adults) of this and related night-flying Actias species, collectively referred to as "moon moths", have long hindwing tails. A "false target" hypothesis holds that the tails evolved to reduce predation risk by bats which use echolocation to locate prey. The moths use the spinning hindwing tails to fool bats into attacking nonessential appendages, with success occurring over 55% of the time. Experiments were conducted with Luna moths with intact wings and with the tails removed. With intact wings, a majority of the attacking bats contacted the hindwing tails rather than the body of the moth; only 35% of intact moths were caught versus 81% for those with clipped tails. The results of this experiment support echolocation distortion as an effective countermeasure.

The parasitoid tachinid fly Compsilura concinnata native to Europe was deliberately introduced to the United States throughout much of the 20th century as a biological control for the gypsy moth (Lymantria dispar) (also known as the "spongy moth"). Researchers reported that when Luna moth larvae were placed outside for about a week and then collected and returned to the laboratory, four parasitic species emerged, the most common being C. concinnata. The researchers concluded that this parasitoid fly causes collateral damage to Luna moth populations.

Luna moth larvae have displayed defenses against predators in late instars by developing spines once they reach about 3&nbsp;cm in length. Unlike other species such as Automeris io, which have chemical defenses much earlier in the larval stage, the Luna moth larvae are left largely defenseless until it reaches this length. However, the absence of a chemical defense allows for the shortening of the larval stage. Automeris io has a larval stage at least twice as long on average as Actias luna, leaving it vulnerable to parasitism.

Host plants

The larvae of Luna moths feed on several different species of broadleaf trees. The larvae do not reach population densities sufficient to cause significant damage to their host trees.

The Luna moth appeared on a first class United States postage stamp issued in June 1987. Although more than two dozen butterflies have been so honored, as of 2019 this is the only moth.

In 2025, the Luna moth was designated on a Non-Machineable Surcharge United States postage stamp.

References

  • Luna moth info
  • Rearing Actias luna
  • Actias luna at www.butterfliesandmoths.org
  • Actias luna at Moths of North Carolina