Field of Science

Ghost Moths and Other Obscurities

During my early years in rural New Zealand, I would often take note of the variety of insect life that could be seen coming to the screen doors at night, attracted by the light from inside the house. Among the most spectacular animals that would sometimes turn up was a gigantic pale green moth, about three inches long as it crawled across the screen. This was the puriri moth Aenetus virescens, perhaps New Zealand's best known member of the moth clade Exoporia.

Puriri moth Aenetus virescens, copyright Nga Manu Images NZ.


The Exoporia is one of the more basal moth groups alive today. The name of the clade refers to one of its most distinctive features: a female genital system with separate external openings for the seminal receptacle and the oviduct, meaning that the male's sperm has to travel along an external groove between the two if it is to fertilise the egg (in other Lepidoptera, there is a single cloacal opening, or there are separate openings but the cavities are connected by an internal duct). Other important features of the clade include dicondylic antennae, with two instead of just one articulations between the antenna and the head, and a male reproductive system without a sclerotised tubular intromittent organ (Kristensen 1978; the males instead have the gonopore opening on a shorter protuberance). Six families are generally recognised within the clade but the majority of species (including the puriri moth) belong to just one of these families, the Hepialidae, commonly known as the ghost moths.

Bentwing ghost moth Zelotypia stacyi, copyright CSIRO.


Hepialids definitely buck the phylogenetic trend among moths. Lepidopterists commonly divide the moth and butterfly order between two main groupings, somewhat self-explanatorily referred to as Micro- and Macrolepidoptera. To some extent, this is merely a division of convenience (the practicalities of working with smaller and larger moths can be quite different) but Macrolepidoptera is also used as the name of a major clade within the order with micro-Lepidoptera then indicated for any lepidopteran not belonging to this clade. By this measure, hepialids are by far the largest micro-Lepidoptera out there (most other examples are unquestionably micro). I've already alluded to the fifteen centimetre wingspan of the puriri moth but this isn't even close to being the largest hepialid out there. The honour perhaps goes to the bentwing ghost moth Zelotypia stacyi of eastern Australia which reaches a wingspan of 25 centimetres, a full ten inches. The larvae of hepialids are commonly borers in live trees; the puriri moth, for instance, gets its name because it burrows into puriri trees Vitex lucens. Other species live as larvae in burrows in soil, emerging at night to feed on pasture or leaf litter, or feeding externally on tree roots. Adult hepialids are short-lived and do not feed, and as such their proboscis is reduced or absent. They may emerge en masse at particular times of year. Following mating, females may scatter their eggs at random during flight or lay them in loose masses on the ground, with larvae finding a suitable food source after hatching. Because of the high mortality rates associated with this scatter-shot method, laying rates can be exceedingly large: females of some genera may produce around 18,000 eggs apiece (Nielsen & Common 1991).

Mnesarchaea acuta, copyright George Gibbs.


The other exoporian families are all much less diverse and more localised. They are also all small moths, far more typical 'micro-Lepidoptera'. The genus Mnesarchaea, endemic to New Zealand, retains functional mouthparts and is believed to be the sister group to all other exoporians. Larvae of Mnesarchaea live in silken galleries among mosses and liverworts, feeding on moss and liverwort leaves, algae, fungal spores and the like. The remaining families all lack functioning mouthparts as adults but their habits are otherwise all but unknown. Anomoses hylecoetes is placed in its own family known from rainforests in eastern Australia. The family Neotheoridae was until recently known from only a single female specimen collected in Brazil, but a few further species of this family were described recently by Simonsen & Kristensen (2017). Prototheora, another genus held worthy of its own family, is found in southern Africa. Finally, the family Palaeosetidae is known from a small number of genera with disjunct distributions in Colombia, south-east Asia and Australia. Because of its scattered distribution, some authors have questioned whether this last family is monophyletic, but an analysis of exoporian phylogeny by Simonsen & Kristensen (2017) continued to support it as such. It is not impossible that this family is more widespread, its apparent rarity due to the overlooking of small moths emerging for only very short periods, living just long enough to breed and deposit their eggs in as-yet-unknown locales.

REFERENCES

Kristensen, N. P. 1978. A new familia of Hepialoidea from South America, with remarks on the phylogeny of the subordo Exoporia (Lepidoptera). Entomologica Germanica 4 (3–4): 272–294.

Nielsen, E. S., & I. F. B. Common. 1991. Lepidoptera (moths and butterflies). In: CSIRO. The Insects of Australia: A textbook for students and research workers 2nd ed. vol. 2 pp. 817–915. Melbourne University Press: Carlton (Victoria).

Simonsen, T. J., & N. P. Kristensen. 2017. Revision of the endemic Brazilian 'neotheorid' hepialids, with morphological evidence for the phylogenetic relationships of the basal lineages of Hepialidae (Lepidoptera: Hepialoidea). Arthropod Systematics and Phylogeny 75 (2): 281–301.

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