Emerging Ghosts
On rainy nights in late Autumn to early Winter we’re often disturbed by the sound of large moths battering against the flyscreens of illuminated rooms. These spectacular insects belong to the family Hepialidae and are commonly known as Ghost Moths.
Our Ghost Moths are survivors!
We were concerned that our ghost moths might not have survived the fire that swept through our forest at the beginning of this year. So we were gratified to welcome them back on at least six occasions in May and June. They appeared on almost every rainy night in those two months.
We sighted three hepialid species on those evenings - Oxycanus dirempta, Oxycanus silvanus and Abantiades atripalpis. On occasion, substantial numbers of ghost moths (up to 30) appeared at the same time.
Adult ghost moths are reported to live for only one day (ref. 1). On that day, they don’t feed. Their sole and urgent task - carried out in the late evening - is to breed.
The mated females drop to the ground and lay huge numbers of eggs, scattering them over the soil surface. We sometimes see female Oxycanus moths on the window screens releasing streams of eggs.
Ghost moths have a protracted larval period
The caterpillars dig a vertical tunnel in the soil after hatching and emerge at night to feed on leaf litter.
The larval stage of the life cycle is long - up to two years! In the best studied species, Oxycanus antipoda, (previously called Oxycanus fuscomaculatus), larvae hatch from eggs in May then pupate in February of the second year (ref. 2).
The adults emerge from their pupal cases in late April/May, leaving the distinctive exuviae protruding from the soil.
A place for ghost moth development
Until recently, we’ve not known where in our forest these events are taking place. The larvae remain hidden in the ground during the day. We’d have been fortunate to find them when they came to the surface to feed at night. But in mid July we lucked out.
We discovered a grove of burnt casuarina trees where the ground was littered with ghost moth pupal cases.
Some were sticking vertically out of the soil, others were lying on their sides.
We were surprised to find the pupal cases here as it has been reported that Oxycanus larvae normally feed under Acacia bushes (ref. 3).
The site of ghost moth development 7 months after the fire
The secret of ghost moth survival
The undergrowth and indeed the whole humus layer of the soil was completely burnt away at the site where we discovered the pupal cases. All that remained of the casuarina trees were charred sticks.
So how did the ghost moths survive the fire?
Working backwards from the time we saw the adults in Autumn, it’s likely that our ghost moths were larvae at the time the fire struck.
They survived the heat of the blaze just by retreating to their burrows. In the case of Oxycanus antipoda, these are up to 25cm deep (ref. 2).
This begs the question of how the larvae managed to survive after the fire, given that their food source, the leaf litter, was destroyed. It’s most likely that they entered the pupal stage prematurely, soon after the fire struck. This would have been just a month or so earlier than normal.
In any event, this is another wonderful example of the resilience of forest life in the face of a natural disaster.
References
Zborowski, P. and Edwards, T. (2007) “A Guide to Australian Moths”. p. 40 CSIRO Publishing
Hardy, R.J. (1974) “The biology and pest status of Oxycanus fuscomaculatus Walker (Lepidoptera: Hepialidae) in Tasmania”. J. Aust. ent. Soc. 13: 317-328
Common, I.F.B. (1990) “Moths of Australia”. Melbourne University Press.
See Kerri’s earlier post for more about ghost moths.
