The Atlas Moth: Hong Kong's Largest Insect

After a search that spanned over two years, I finally had the opportunity to see an Atlas Moth (Attacus atlas) up close. My interest began in 2023, when I first encountered a Lesser Atlas Moth. Since then, observing the larger and more renowned Atlas Moth became a personal goal, if not a bit of an obsession.

Understanding that Atlas Moths are nocturnal, I dedicated many evenings to hiking and searching, always returning without success. That changed unexpectedly just a few weeks ago in July 2025. While attending a birthday gathering in Sai Kung, I noticed a male Atlas Moth resting quietly by a small light.

I had always expected to see the Atlas Moth in some remote woodland, or while on an adventure far away from the city lights, but the moth had other plans, I suppose.

I could scarcely believe my luck as I did my best to photograph it while causing minimal disturbance.

This particular moth was a male, and therefore only measured in at around 15cm, or half a foot from wingtip to wingtip. Females usually double in size and can reach 30cm, or just under one foot in total.

It was genuinely a wildlife encounter I will not forget!

• One of the largest moth species in the world, with a wingspan up to 24–27 cm (9.4–10.6 inches), rivaled only by a few species like the white witch and Hercules moth.
• Largest wing surface area of any moth, reaching about 160 cm² (25 in²), giving them a strikingly impressive appearance.
• Males and females differ significantly in size and antennae: females are larger and heavier, while males have broader, bushier antennae used for sensing pheromones. The sole goal of the moth is to reproduce, the act of which can last up to 24-hours. Females will then lay up to 150 eggs before dying.
• Adults have non-functional mouthparts and do not eat, relying entirely on fat reserves built during the larval stage to survive their short adult lives that last only a few days to two weeks. They grow more sluggish and lose coloring as they age.
• Larvae consume massive amounts of leaves from trees like citrus, cinnamon, guava, and others to build up energy for metamorphosis and adult life.
• Their caterpillars are notable for distinctive waxy spines and color patterns, including a bright orange ring on the last abdominal segment that helps identify them. They also produce irritants that prevent them from being predated upon.
• Their cocoons are large and papery, often incorporating dried leaves and silk, and can be up to 7–8 cm long.
• The wings' edges mimic the head of a snake, specifically a cobra, a feature thought to help deter predators by resembling such a dangerous animal.
• Atlas moths live primarily in tropical and subtropical forests of South and Southeast Asia, where they thrive in warm, broad-leafed evergreen habitats.
• They are unsteady, weak fliers, preferring to stay still unless locked in on finding a mate. The females do not venture far from where they emerge from their coccoons.

Life Cycle

• Egg stage: Females lay several spherical eggs on the undersides of host plant leaves. Eggs hatch in about 1 to 2 weeks (7–14 days).
• Larval (caterpillar) stage: After hatching, the caterpillars feed heavily on leaves of plants such as citrus, guava, cinnamon, and evergreen trees. They go through five to six instars (growth stages separated by molting). The larval period lasts approximately 4 to 6 weeks before pupation.
• Pupal stage: Caterpillars spin a large, papery cocoon (7–8 cm long) interwoven with dried leaves, usually attached to a twig. The pupal stage inside the cocoon typically lasts about 4 weeks (around 28 days), depending on environmental conditions.
• Adult stage: Adults emerge in the morning and spend 8–10 hours expanding and hardening their wings after emergence. Atlas moths are nocturnal and primarily active at night. Adults have non-functional mouthparts and do not feed, relying on fat stored from the larval stage. Their adult lifespan is short, generally around 5 to 14 days, with mating and reproduction as their sole purpose.

Behavior

• Adults are mostly stationary after emergence to conserve energy, focusing on locating mates.
• Females release pheromones to attract males, which use their large, feathery antennae to detect these scents.
• The entire life cycle from egg to adult moth can take roughly 8 to 10 weeks in total, varying by environmental factors.

Atlas moths in Hong Kong are most active and visible during the warmer months, specifically from May to September, though they can sometimes be seen into November.

They are most frequently encountered in forested areas, and occasionally can be found around human dwellings where they are attracted to lights (as was the case with the moth I photographed). You might spot them in places like Sai Kung, Tai Po Kau Nature Reserve, Kam Shan Country Park, and Tai Mo Shan Country Park.