Insects forecast the Weather: Might this be a Rain Moth from Australia???

Subject: Giant Wood Moth?
Location: Ballarat, Victoria
April 11, 2016 5:25 pm
Found this giant late evening in Ballarat, Victoria.
Smaller one seen the night previous. Another visitor from our Northern States?
Signature: HB

Female Rain Moth we believe
Female Rain Moth we believe

Dear HB,
We have done a bit of research, and we are not certain we are correct, but this is the best we can do.  Wood Moths, also known as Goat Moths and Witchetty Grubs are in the family Cossidae.  We classify them on our site together with Ghost Moths or Swift Moths in the family Hepialidae because we have trouble distinguishing members of the two families from one another.  We believe your moth is a Rain Moth,
Trictena atripalpis, a species we first located on an April 7, 2016 posting on The Advertiser which states:  “NATURE is making its own weather forecasts in South Australia’s parched South-East, where the giant “rain moth” has arrived ahead of the Bureau of Meteorology’s own predictions of drought-easing falls this week.  Large numbers of the trictena atripalpis moth, which has a wingspan up to 16cm, have been reported in Keith, Kingston, Penola and Mount Gambier and farming mythology has it that the insects bring rain.  Science backs this to some extent, as the creatures grow from ground-dwelling “bardi grubs” and are most likely to emerge from the earth when autumn rain is in the air.  Bureau of Meteorology duty forecaster Hannah Marsh said a series of fronts were expected to move across the South-East over the next few days.”  According to NatureOutWest:  “The large moths emerge from their holes in the ground after rains. They are frequently seen when they are attracted to lights. They are so large they almost resemble small bats or birds as they flutter around lights at night.”  Though we missed it the first two times we scanned Butterfly House, once we had a scientific name from the previous two sites, we learned that “The moths have grey-brown wings with two variable ragged silver flash markings across each forewing. The forewings often also show intricate sinuous patterns of pale lines. The wingspan of the males can reach 12 cms. That of the females can reach 16 cms. The moths have tripectinate antennae.”  We suspect that only the male Rain Moths or Waikerie may have the “ragged silver flash markings” and also that they have the more developed “tripectinate antennae” to locate the female when she releases pheromones, and we also believe that all the individuals pictured on Butterfly House are males, though the site makes a point of stating:  “The adult females deposit large numbers of eggs. Indeed, this species holds the World Fecundity Record, for the greatest number of eggs being deposited by a non-social insect. One dissected female had 44,100 eggs. It is thought that the eggs are laid in flight, just being scattered across the ground.  The moths a famous for being able to predict rain. In some areas in autumn, the moths appear on only one night each year, yet all appear together in droves, and always just a few hours before a major downpour in that area. Perhaps the rain helps wash the scattered eggs into crevices in the ground, as well as dormant seeds to germinate, so that after the eggs hatch: the young caterpillars can easily find roots on which to feed.”  Your moths both have much slimmer antennae, leading us to believe they are both females.  This image on FlickR supports our supposition.  Forecaster Hannah Marsh was quoted on The Advertiser as stating:  “A strong low-pressure system will pass well to the south of Tasmania on Sunday with a cold front moving over the southern coasts of the state,” she said.  “Those fronts will bring gradual shower activity for the next six days.”  We would love to know if the weather forecast was correct, and if any male Rain Moths with more spectacular antennae arrive at your porch light, we hope you will send us additional images.

A smaller female Rain Moth, we believe
A smaller female Rain Moth, we believe

Dear Daniel,
Thank you for your prompt and very informative reply,
We have had no rain sadly as we could’ve done with a good soaking but nonetheless happy to be visited by such an interesting creature. A few days before this beauty showed up out the rear of the property.
Ive sinc

4 thoughts on “Insects forecast the Weather: Might this be a Rain Moth from Australia???”

  1. Note no ‘wood or goat’ but therein lies a problem with common names – especially in Australia.

    The ‘several species’ are actually hundreds and witjuti (wichetty) applies across moth families and also includes some beetles. Basically any fat, edible larvae from wood or ground will do 🙂

    ‘Bardi’ and ‘Rain moth’ are common but may be localised to different states.

    Hepialidae have a Gondwanan distribution are mostly called ‘Ghost’ or ‘Swift’ moths in Australia.

    To HB’s original message.. these moths (like many Cossidae) are large and heavy and their life-cycle means they are unlikely to be ‘blow-ins’ from other states.


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