Lee Kong Chian Natural History Museum

Attacus atlas Linnaeus, 1758

Kingdom:Animalia
Phylum/Division:Arthropoda
Class:Insecta
Order:Lepidoptera
Family:Saturniidae
Genus:Attacus
Species:A. atlas
Common Names:Atlas Moth
Status:Common

Description

Both sexes have big patterned reddish-brown sickle-shaped forewings and hairy bodies that are disproportionately smaller than the wings (wingspan 23 cm). The larger females are the largest moths in the world in terms of wing area. 

Read more about the Lepidoptera order.
Read more about the Saturniidae family.

Locality Map

General Biology

The Atlas Moth is supposedly the largest moth in the world. The adult does not have mouthparts to feed and survives on the fat reserves built up during the larval stage. The newly emerged female often remain still or moves to an open spot where its powerful pheromones can be dispersed by the wind. Males can detect the pheromones kilometres away with their larger and bushier pair of antennae. The female is larger than the male.

The caterpillars feed on a variety of tree foliage, reaching up to 12 cm in their final instar and have long spines covered with a white sticky powder. The cocoons made up of broken strands of silk have been used to make silk in some countries.

Diet

The caterpillar eats a wide variety of plants, including Barringtonia asiatica, Muntingia calabura, Citrus hystrix, Citrus spp., Averrhoa carambola, Macaranga hyeni, etc.

Life Cycle

The eggs are oval, 2.0–2.5 mm, sticky, light brown and with a few, darker longitudinal bands. They are laid individually or a few clumped together. The total number of eggs laid per female can be up to 200 or more.

The egg hatches about nine days later and the 7 mm greyish caterpillar emerges with a black head. Within a few days it turns white with orange blotches and the head gradually turns orange, then grey-green. Numerous long spines cover the body. A few of these spines around the head and thoracic region turn black with age. The three pairs of segmented thoracic legs are black, each ending in a terminal tarsus with a curved claw. The pairs of abdominal prolegs on segments 4–7 and 10 are fleshy, white, turning green as the caterpillar ages. The apices of these prolegs bear a series of crochets. The last segment of the abdomen bears a pair of claspers, eeach with a roundish orange patch.

The first moult occurs at 4-6 days, the second 10-22 days, the third 26-29 days and the fourth and last pre-pupa moult at 49-57 days.

As the caterpillar grows to around 40 mm in length, about 30 days or more old, the sides turn green while the dorsal region remains white, covered with prominent small black dots. The last segment of the abdomen has green-blue dots and bears the shape of a snake's head with the two orange patches appearing as eyes. The abdominal prolegs bear a pair of black bands each. the maximum length of the caterpillar is around 80 mm in the relaxed stage. The last moult takes place around 49-57 days after which it keeps on eating until about 62-72 days when it becomes restless, moving along the branches seeking out a suitable place to pupate. Once it has located a leaf, it begins to lay a layer of silk on its surface, to move around silking the point of attachment of the leaf to the branch and finally covering itself with silk with the leaf edges wrapping round itself. It remains thus for 62-70 days. About 12 days after pupal forming, the caterpillar undergoes a final moult inside the pupal case.

Eclosion occurs 22-29 days after the start of pupating, at any time of the day or night, but mostly during the early hours of the morning. The only sign of eclosion is scratching from within the pupa. The moth suddenly crawls out from the upper end of the pupa where the silk covering is loose. Once out, it crawls to the bottom of the pupal case and hangs out its wings by pumping air through them. This takes about two hours before the wings are fully extended and functioning.

Apparently the male ecloses a few days earlier than the female. Once out, it remains attached to the pupal case until the following night before flying off. In the case of the female it remains where it is and receives the visiting males. Up to four males have been observed to visit but only two have the opportunity (and space) to cling on to the body of the female. Of these two, only one eventually mates with the female, the pair remaining attached for up to more than 24 hours. Once the pair detaches from each other, the pair will fly off and the female will start to lay her eggs on the leaves of a suitable food plant.

References

Chua, M. A. H. 2011. Saturniid moths. Pp. 441. In: Ng, P. K. L., R. T. Corlett & H. T. W. Tan (editors). Singapore Biodiversity. An Encyclopedia of the Natural Environment and Sustainable Development. Editions Didier Millet, Singapore. 552 pp.

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