The Bogong moth is one of the most interesting insects in Australia. It has a brown to black body with a wingspan of up to 5 centimeters, (2 inches). It can be recognized by the unique markings on its wings. It has a dark arrow shaped spot, a dark comma shaped spot and a lighter spot all on the top two wings. The bottom two wings are a lighter beige color with a dark brown trim. The moth's life story is actually very captivating. The eggs are laid at the base of plants in New South Wales and Queensland. Four weeks later a light brown to black coloured caterpillar breaks out of the egg. It hides during the day in the soil or under fallen leaves and plants and feasts at night. Farmers consider these caterpillars pests and have named them cutworms because they cut pieces of plants to bring them in their homes to eat. Their diet varies between cereals, peas, cauliflower, cabbage and alfalfa. These caterpillars grow to be about 5 centimeters, (2 inches), long and then form a cocoon around themselves in the homes they have made for themselves. After four more weeks the moth finally emerges from the cocoon.
When the summer months are just around the corner the moths decide that it is time to migrate to a cooler environment. They start a journey of up to 3 000 kilometers, (1865 miles), to caves in the Australian Alpes. Tens of millions of these moths together start their journey together. There have been problems in cities that are on the flight path. It seems that since the moths fly at night each time they come upon a city the moths confuse the city lights with the sun rising and swarm the cities trying to find dark hiding places. Entire walls of buildings are covered in moths. Eventually they find their way to the Alpes where they spend the summer months huddled on walls and floors of caves. Many animals come to these caves during those months, as the aboriginals had done before, to feast. The moth's body is 60% fat and very nutritious. It is because of this fat in their bodies that the moths can migrate without even feeding once. When the summer months are over the survivors make their way back to the plains to lay their eggs and then die so that the cycle can start all over again.
There is still a festival dating from the times when Aboriginals went to the caves to feast on moths held every year on the last Saturday of November called the Ngan Girra Festival where 5000 people get together to celebrate.
Bogong moths have been eaten by native Australians for thousands of years, but now the following information has come to light:
The annual migration of bogong moths is bringing toxic levels of arsenic to caves in the Snowy Mountains, scientists have discovered.
Each moth has a small amount of arsenic in its system. After migrating from farmland in New South Wales and Queensland, they gather in the caves in their billions, many dying and falling to the ground.
Last year, with heavy rains, the moths' bodies were washed out of the caves and the accumulated arsenic killed all the vegetation outside.
"I don't think there is a record of similar movement [of arsenic] anywhere else in the world," said Dr Ken Green, wildlife ecologist with the New South Wales National Parks and Wildlife Service, who noticed the dead vegetation earlier this year.
At this time of year where I live in New England we get Bogong Moths flocking to the lights of our house at night, and in the morning they are still here. Some are food for the birds, other hang on to life tenaciously.
This one about five and a half cm long or 2 1/4 inches.
Ken Green: OK, well they do generally come from agricultural lands. The arsenic source, we're not too sure, there's not that many arsenic compounds currently used in agriculture, but it was the pesticide of choice up until about the 1950s, 1960s, when DDT came in, and it's quite possible that arsenic, in fact it's quite likely that arsenic is still in the soil. The moths are picking it up as they feed and then when they concentrate in the mountains in their billions, these small amounts of arsenic are being concentrated.
Paul Willis: While you've got high arsenic levels for Bogong moths in the Snowy Mountains, at other sites in the ACT and in Victoria that also have high concentrations of Bogong moths, you didn't get those high levels of arsenic.
Ken Green: Yes, that was quite interesting, because it's always been postulated that perhaps the moths in particular mountain areas come from different sources. They do have a definite migration pattern and perhaps these moths are going from Point A out west, to a particular mountain peak. If that is the case then it looks like this arsenic is being brought into only particular mountain peaks by particular moths from particular areas.