Leptocneria reducta (Walker, 1855)
White Cedar Moth
(one synonym : Lymantria aurivillii Bryk, 1934)
LYMANTRIIDAE ,   NOCTUOIDEA
 
Don Herbison-Evans,
(donherbisonevans@outlook.com)
and
Stella Crossley and Mark Peaty


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

This caterpillar is all too familiar to people who have a

  • White Cedar or Cape Lilac tree ( Melia azedarach, MELIACEAE ),

    near their home. The caterpillars live communally. By day, they hide in crevices on or near the ground. In the gloom of an evening, they swarm as a seething mass of hundreds of hairy brown bodies, undulating in eerie silent flow up the tree trunk and along the branches to the leaves, which they eat voraciously. Before dawn, they descend again to their daytime shelter. The caterpillars feed communally on the foliage of their tree, and when a tree becomes defoliated, they wander everywhere looking for another one, and so they invade homes, garages, sheds, cars, anywhere, in their search.

    If you detect the infestation of a tree before they go walkabout, then wrapping a rag around the trunk soaked in sump oil will deter them from their dusk ascent, and starve them.

    If they are mature, and have been coming into the house already by crawling under doors, then you can deter them from entering the house by spraying Insecticide Surface Spray along just under each door.

    They only do the walkabout for a week or so, after which most will have found some nook to stay in, after which you can relax for the next 51 weeks.


    (Photo: courtesy of Simon Mountfort, St. Ives, New South Wales)

    The caterpillar is dark brown, with orange feet, and a dim yellow line along the back. It grows to a length of about 4 cms. It has two small brown knobs on abdominal segments six and seven, which are dorsal glands. It is covered in bristles, to which some people are allergic, giving them Urticaria. Not only do humans suffer from irritation from the hairs. The hairs have also been implicated in causing abortions in horses.


    Despite the total defoliation of a tree by these caterpillars every year, the affected White Cedar trees seem to thrive quite happily. Presumably this is because they are deciduous, and so would lose their leaves anyway.

    The camouflage of of the caterpillars is quite amazing, in that at each stage of the larva's growth, its colouring and other features [for example segmentation] seem to closely match same size features of the bark.

    The caterpillars seem to have few competent natural predators. Many birds such as Magpies and Magpie Larks show no interest in the stragglers still on the lower trunks of trees in the light of morning, but Tawny Frogmouths (Podargus strigoides) and Fan-tailed Cuckoos ( Cacomantis flabelliformis) have been observed eating them.

    The main enemy may be wasps, but the local native wasps just don't seem to have it together when tracking the caterpillars down, but they do seem to be seeking them. The wasps can find the bodies of the squashed caterpillars, so perhaps the wasps are going by the smell more than anything else.

    The main cause of mortality seems to be starvation. Every year, many caterpillars may be found in winter in ground debris and crevices near a tree, and only a few make it to pupation. Whether the overwintering caterpillars survive long enough to take advantage of the new foliage in the following spring is unknown.


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

    Pupation occurs in a large oval cocoon in the leaf litter. The pupa is brown and hairy too. The discarded hairy skin of the Caterpillar is usually alongside the pupa in the cocoon. The hairs in the cocoon can also cause urticaria in susceptible people.


    female
    (Photo: courtesy of John Stumm)

    The adult emerges after a few weeks in summer, or sometimes does not emerge until the following spring. It readily comes to lights at night in warmer weather. The moth is grey, with two dark spots near the middle of each forewing. The dark spots are bordered with orange in live specimens, but the orange colour fades to grey when the insect dies. The hindwings are a pale grey, each with a dark mark.


    (Specimen: courtesy of the The Australian Museum)

    The male and female moths have similar coloration, but the female has more spindly antennae, and is larger. The female has a wingspan of about 4.5 cms, the male about 3.5 cms.


    male
    (Photo: courtesy of John Stumm)

    The moths when disturbed are inclined to play 'dead' for up to 20 minutes.


    playing dead
    (Photo: courtesy of John Stumm)

    The moths are remarkably efficient at locating White Cedar trees. A friend has a White Cedar tree he planted himself several years ago, which struggled for some years to find water in the clay soil. Last season its roots must have found the water table because he said it finally 'took off', and promptly got infested with these caterpillars! He reckons his property is about 25 acres and he knows of no other Cape Lilac tree on neighbouring properties. The caterpillars are found all over Australia, wherever White Cedar trees grow.

    White Cedars are poisonous to most animals including most other caterpillars. Indeed: extracts of the plant have been proposed as as a natural insecticide. Over millions of years, these caterpillars seem to have co-evolved with the White Cedar, developing an immunity to the poison, which in turn probably makes them poisonous and less vulnerable to predation.


    eggs
    (Photo: courtesy of Kathy Wheeler, Lavington, New South Wales)

    The caterpillar starts life as one of a neat geometric array of eggs, laid under a foodplant leaf or on the trunk or indeed anywhere nearby, like in a house if the moth happens to have emerged in the house, having walked in as a caterpillar and pupated there the previous year.


    underside
    (Photo: courtesy of Joan Fearn, Milton, New South Wales)

    In Sydney, counts were made of the number of adults coming nightly to an ultra-violet light, and the numbers totalled for each month of the year :

    JanFebMarAprMayJun JulAugSepOctNovDec
    7
    97
    19
    4
    2
    0
    0
    0
    7
    11
    0
    14

    The double peak (in February and in October) indicates that there are two generations a year.

    We have received reports of this species being present over most of mainland Australia, including:

  • Northern Territory,
  • Queensland,
  • New South Wales,
  • Victoria,
  • South Australia, and
  • Western Australia.


    Further reading :

    David Carter,
    Butterflies and Moths,
    Collins Eyewitness Handbooks, Sydney 1992, p. 270.

    Ian F.B. Common,
    Moths of Australia,
    Melbourne University Press, 1990, fig. 43.9, pp. 70, 429.

    Francis Walker,
    Catalogue of Lepidoptera Heterocera,
    List of the Specimens of Lepidopterous Insects in the Collection of the British Museum,
    Part 4 (1855), p. 888.

    Paul Zborowski and Ted Edwards,
    A Guide to Australian Moths,
    CSIRO Publishing, 2007, pp. 177, 179, 180.


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    (updated 24 June 2013, 5 March 2015)