Question: Has the emperor gum moth declined in numbers recently?
Answer: The Emperor Gum Moth, (Opodiphthera eucalypti), is a spectacular species of moth that is found over most of Australia and has been introduced to New Zealand. It can be quite variable in colour ranging from grey, through straw-coloured, to almost brick red.
The caterpillars feed on a variety of species of gum, but will also feed on other plant species. The caterpillars need to consume enough food to complete the transition from caterpillar to moth and also to sustain the adult moth as the adults do not feed.
While the larvae of this species can cause some damage to trees with their eating of the leaves this species is not usually associated with widespread damage. The Emperor Gum Moth is a food source for large birds and is also parasitised by a number of insect species.
This species of moth used to be commonly seen in the larval form, as the caterpillars are large and quite spectacular with their colour scheme and spiky protuberances. Anecdotal evidence suggests that the caterpillars were more common a generation ago and the question has been raised as to the availability of any studies or proof that the numbers of this species are falling. While we have not been able to find any concrete evidence of their decline, some people of an older generation have reported that the moths both in the adult stage and as larvae are much less common now than when they were children.
The European Wasp is a predator of many native species including the Emperor Gum Moth caterpillars. The Senior Curator of Entomology at Melbourne Museum believes that the European Wasp has unfortunately had a huge impact on the population of this species in some areas.
The staff in the Live Exhibits Department have suggested the best thing is probably to leave them where you saw them. Some of the individuals may not survive but hopefully enough will make it to adulthood to breed.
The Emperor Gum Moth is a species that is native to Australia and has been introduced to New Zealand. We are not aware of it being officially recognised as being present in America. If you are able to take some good quality images please feel free to send them to firstname.lastname@example.org and we will have a look at them for you. Alternately you may also want to contact your local Museum to see whether there are any moth species in Michigan which may appear similar.
Hi Barry, we didn't receive any images from Brenda. You are correct that a number of Australian insects such as longicorn beetles and some weevil species cause damage to Eucalyptus plantations in America. This is because many of the predators that help to keep their numbers under control in Australia are absent in America. Other Australian insects such as the Cottony Cushion Scale have also made it to America and cause damage to the American citrus industry.
Hi Andrea, if you still have the moth, capture it with a large container so as not to damage the wings, and release it outside.
One thing you need to keep in mind with Emperor Gum caterpillars is that they will readily drown themselves in jars of water you might use to keep the branches in. Make sure the top of an open jar holding branches is blocked by sponges or something similar that the caterpillars can’t get past.
Good to hear from you again. As a population, Emperor Gum Moths seem to have a built-in range of emergence times, so some will emerge sooner, others later, some in years that are good for moths and others in years that are not so good. This way they hedge their bets against bad years and the overall population survives and, particularly in the good years, prospers.
In a good summer, however, especially an early warm summer, the first generation may go through its life cycle quickly, leaving time for a second generation before autumn.
This means they can emerge from the cocoon in as little as a month, although this is rare. As you've said, it's more likely to be between 4 months and 1-2 years.
Keep up the good work.
Hi EJ, Brenda from Michigan asked a similar question on the 25th Mar 2010. Please have a look at the answer we posted for Brenda.
We love receiving comments, but can’t always respond.
Hi Diane, Museum Victoria has a free Identification Service. If you send us a photograph of your caterpillars, we would be happy to identify them for you. Large numbers of caterpillars feeding on a single young tree may cause the tree to become stressed. However, if the tree is otherwise well-established and healthy, it should recover.
Small parasitic wasps often attack Emperor Gum caterpillars, but they tend to have an effect only in the later stages of development. The caterpillars are also susceptible to disease such as nuclear polyhedral viruses, but the symptoms for these are very different to those you described.
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