Bombyx mori

Bombyx mori (Linnaeus, 1758)
Domestic Silkworm
(previously known as : Phalaena mori)
BOMBYCIDAE, BOMBYCOIDEA

Don Herbison-Evans
(donherbisonevans@yahoo.com)
and
Stella Crossley

early instar, drawing by Harold Maxwell-Lefroy,
Indian Insect Life: a Manual of the Insects of the Plains, 1909, Plate XXVIII, Fig. 9,
image courtesy of Biodiversity Heritage Library, digitized by NCSU Libraries.

Early instars are off-white and hairy. As the caterpillar matures, it loses the hairs and becomes smooth. The mature caterpillars are buff coloured, with a horn on the tail and brown marks on the thorax. The caterpillars grow to a length of about 4 cms.

mature caterpillar
(Photo: courtesy of the Macleay Museum, University of Sydney)

Silkworms are the Caterpillars of the Silkmoth. They were introduced by European settlers into Australia in the nineteenth century to try and create a Silk industry (sericulture). Attempts are still being made to set up a sericulture industry in Australia. Silkworms are also used for educational purposes. The growing of silkworms and the making of silk is extensively illustrated in the BBC video "War of the Worlds", in the "Alien Empire" series. The caterpillars were originally tamed in China, and are now so domesticated that they cannot even hang onto the leaves of their food plant, but have to be kept in cages and have food leaves given to them. The tale of their domestication is part Chinese Folklore.

stylised silkworm earings

The caterpillars are often fed on the leaves of plants from MORACEAE, including

White Mulberry ( Morus alba ),

Black Mulberry ( Morus nigra ),

Red Mulberry ( Morus rubra ), and

Che ( Cudrania tricuspidata ).

Young caterpillars will only feed on very young leaves.

Commercially, the leaves are ground and fortified with flour to make Silkworm Chow. The caterpillars are reported to accept Lettuce, but decline Spinach.

(Photo: courtesy of the Macleay Museum, University of Sydney)

The caterpillars pupate in a substantial cocoon, which may be nearly any shade depending on their food and genetics. The thread from a single silkworm cocoon is about 1 Km (10^3 m) long and has a diameter of about 7 microns ( 7 x 10^(-6) m) with a density close to 1.3 x 10^3 Kg/m^3. So a single thread weighs about pi x 3.5^2 x 1.3 x 10^(3 -12 +3) ~= 5 x 10^(-5) Kg. So 1 Kg silk would be produced by approximately 1/(5 x 10^(-5)) = 20,000 silkworms.

Male
(Specimen: courtesy of The Australian Museum)

The adult moths are buff coloured, with pale brown lines. Again, the domestication has been so complete that the moths cannot fly. They also have degenerate mouthparts, and so cannot feed. They are totally reliant on the nourishment ingested in their earlier caterpillar stage. The moths have a wingspan of about 4 cms.

Female, with cocoon and eggs
(Photo: courtesy of Merlin Crossley)

The females lay several hundred eggs, which hatch normally in spring. The eggs are white and ellipsoidal, with a length of about 1 mm. The eggs may be kept indefinitely in a refrigerator (not a freezer: that kills them) allowing broods to be obtained at any time of year.