In Canberra, the heavy rains of March and April bring out a large and spectacular Hepialid, Trictena atripalpis (Walker, 1856). It is quite common and the larvae are the famous bardi grubs used for fishing bait, especially in the Murray River basin. Another common name for this species, Waikerie, is the origin of the town of the same name in South Australia (I have to collect some Trictena from there one day!). Common though they may be, there is something special about Trictena, and I love having such large moths living in my yard (they can get to 180 mm). I call them big moths out of affection.
Here is a representative male, photographed here in Canberra on 28 April 2013 (although this male is maybe a tad more silver than usual):
And a newly eclosed female from the same locality and date (perhaps a little on the darker side of possible variation):
As currently defined, T. atripalpis has a huge distribution extending from southern Queensland through New South Wales, Victoria, South Australia and Western Australia. However, there are a bunch of cryptic species under the umbrella of T. atripalpis. I have specimens collected at Ceduna, South Australia, and Rainbow, Victoria, by very dear friends and all round great guys Nick Temby and Fabian Douglas that can be sorted into at least four or five entities based on antennal colour and forewing ground plan (the moths, not Nick and Fabe!). My understanding is that the forthcoming monograph on Australian Hepialids by Thomas Simonsen will erect a number of new taxa from T. atripalpis alone.
The usual suspects gathered around the light at 5 AM on 3 April 2014. This is a usual moth night for me.
I don’t have to go far to collect T. atripalpis – in fact, all I need do is turn on a moth light in my yard. However, any light will attract some Trictena if they are about, and they come knocking on the windows and doors for numerous people in rural and semi-rural parts of Australia. In fact, the moths are so sociable that Fabian, Nick and I talk of them knocking at the doors and windows to be let in out of the rain! To me, this is a wonder of nature and it is a privilege to experience it (although some people do get seriously freaked out by them).
The usual pattern for me is that the adults emerge on dusk, leaving pupal cases like these poking out of the ground:
Pupal exuviae like these are usually the only sign to the uninitiated that there has been a big moth night. But most people mistake the pupal cases for something else, such as fungi or even cast reptile skins.
Around 8-8:30 PM AEST, the first specimens will arrive with a loud thump at the window, followed by a frantic patter of wings flapping as they struggle to get to the light source that attracted them. They are rather dopey around lights and will settle quickly, becoming very docile once they cool down.
Some females at the moth light, again at 5 AM on 3 April 2014.
As the night wears on, fewer specimens come in, dropping off around midnight. But the numbers increase in the hours before dawn, and this is usually when females arrive.
As with a number of other Hepialids, T. atripalpis fly with their longitudinal axis held at about a 45-degree angle to the ground and the tip of their abdomen raised. Their wings have a shallow arc and whirr madly. This means that a lot of specimens attracted to lights are rather battered, especially females which arrive in the early hours of the morning (one flying in as late as 6 AM in April last year!). The best female I have (pic above) was one I collected shortly after it had eclosed in my yard. The females scatter eggs as they fly. By dawn, their lives are over and birds will quickly polish up any moths left over. Aside from the pupal cases, a few spent wings are the only sign that these majestic moths have been and gone:
The remains of Trictena cleaned up by birds in my garden after a moth night.
We still don’t know what the newly hatched larvae feed on in the wild, or how they transition to a life of girdling Eucaltypus roots deep underground. That this mystery repeats itself year after year in my yard and I still remain oblivious after trying to get larvae to feed (on carrots, mushrooms, paper towel[!], etc) in captivity, or find them in my garden, is a source of both deep frustration and wonder.
March was relatively dry here, but the long weekend (Easter) looked to be very promising for rainfall – at least initially. Then the forecast alternated day by day as to whether it would rain. Eventually, the weather forecasters let themselves down badly and we got less than 1 mm over Easter.
Then, finally, Dorothea Mackellar’s poem My Country once again rang true:
But then, the grey clouds gather, and we can bless again.
The drumming of an army! The steady, soaking rain!
And it was a big moth night once more.
But typically, it happens on the night of Easter Monday (6 April; why, why, why could it not have happened over the weekend proper?), so I will be guaranteed to arrive at work feeling very tired. That it then happened again the night after (Tuesday 7 April) means I am absolutely wrecked as I write this on the night of Wednesday 8 April…
Monday 6 April:
8 PM – it is raining and the moth lights are on in anticipation!
I use compact fluorescent lamps at home to attract moths. They are sold at Bunnings (= Home Depot or Lowes for those in North America) under the Gecko brand name. 50W tubes are far and away the best, and you can run them under wet and cold conditions that would shatter mercury vapour (MV) bulbs. They do put out a LOT of UV, so safety glasses that block at least 380nm and below are needed. Polycarbonate lenses are a good choice.
9:30 PM – well this is odd – no moths yet!
10:15 PM – still no moths. Time to go check the nearby service stations to see whether I am being hexed here at home.
10:45 PM – nothing at the service stations, but joy of joys, look what was waiting for me at home!
Two beautiful and fresh males! But normally there would have been at least six by now. Something isn’t right…
I set them – they are magnificent specimens – and go to bed. Note the white under the abdomen of the lower specimen? This is some paper towel folded into layers and used to support the abdomen. This is a good idea for setting Hepialids, as they leach grease like crazy (Cossids are equally bad)! Because Trictena and Abantiades are such strong fliers, their wing muscles are very powerful and make setting the wings difficult, because the muscles keep pulling the wings out of square. I set my Hepialids using clear mylar setting tape as coverstrips to tension the wings, and 000 ento pins inserted through the mylar tape into the thicker veins on the forewing and hindwing, which are very robust on these genera and provide good anchorage points. Provided you remove the 000 pins before the setting tape is de-tensioned, they come out cleanly and the holes are hardly noticeable.
I will have to post a setting tutorial because setting Exoporia requires a different strategy to non-Exoporian Lepidoptera. The Jugum is a key reason for this and makes setting frustrating if you don’t understand how it works. In fact, the jugum can undermine your setting attempts – it is possibly why many people set Hepialids with a gap between the fore- and hindwings that looks awful IMHO. But there are some tricks I have learned from setting numerous specimens of Oxycanus and Trictena that make it easy – once you know the morphology works and how to exploit it.
Tuesday 7 April
1 AM – I automatically wake and drag myself downstairs to go check the light again – no new additions. I slip into that awkward sleep that comes from knowing there is an alarm due to go off all to soon and after an uncomfortable, fitfull and dreamless sleep…
5 AM – <phone alarm vibrates> Bleeaaaaargh!
I drag myself out of a nice warm bed into 6*C rain.
Waiting for me are four more males, of which three are keep-able, and one really battered female that shows the unusual semi-translucency that worn T. atripalpis specimens get. I keep her to show this in the collection (and to get some eggs to scatter under the Eucalypt in my yard) and to record females were actually flying. Bizarrely, she does not lay, which implies to me that she is unfertilised. How bizarre! Every other female I have ever handled has dropped hundreds of thousands of eggs that, despite best efforts to collect and re-sow them under host plants, wind up in crevices on setting boards. These then become wandering larvae that trail silk over everything they cross and necessitate a thorough cleaning out of the moth room. I will dissect this female when the dissecting microscope I have brought arrives. But I am wondering if this hatch was asynchronous – with adults emerging out of sync with each other.
Night of 7-8 April
The Bureau tells our local TV stations that the overnight rainfall was the heaviest recorded for April in 29 years. We got just over 39 mm here, which is wonderful for the garden. But no moths. I suspect that the wind chill factor (2.7*C at 5 PM when these moths usually emerge) might have something to do with it. In fact, the wind chill dropped to 1.7*C when the female moths should have been peaking. The Brindabella Ranges above Canberra also recorded 20 cm of snow. Normally, the low pressure systems and troughs that trigger Hepialid emergences raise the ambient and wind chill temperatures, and do not produce snow. So I suspect the no-show was due to the cold conditions. I did not find any pupal cases, either, which suggests something we do not yet understand tipped the Heps off that this night would not be good for them to emerge.
The only thing that came in was a male of the Anthelid Chelepteryx collesi, the white-stemmed gum moth. It was waiting on the light at 1 AM when the temperature was 6.5*C and wind chill was 2.5*C. Here is an example of this species I photographed here in 2013:
Pretty, but not a Hep. It also has a thick woolly jumper that allows it to handle the cold. Interestingly, this species has sharp processes on the sides of the thorax that, if you try to crush the thorax like you would to immobilise a butterfly, will painfully dig into your thumb and forefinger. I wonder if this is an anti-bat device, as it would presumably be painful for the mucous membranes of the mouth.
Maybe the next rains will be better.