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Byron Shire
April 23, 2021

Lemon Migrant butterfly migration underway

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Lemon Migrant butterfly, also called the Cassia Butterfly. Photo Kath Vail.

Kath Vail

Butterflies have been an important part of mythology for people around the world, from the Egyptians to the Native American Indians. In the Northern Rivers you may have noticed the Lemon Migrant butterfly is currently experiencing a boom in numbers as they migrate down the east coast of Australia.

The first specimens of the Lemon Migrant butterfly were collected when The Endeavour was beached at Cooktown.

The boom of Lemon Migrant butterfly, also called the Cassia Butterfly, at the moment is simply amazing. They look like lemon satin ribbons as they fly briskly through gardens and open habitat.

One off boom

This boom is a one off result of the long drought we’ve experienced across Australia. The females of this species of butterfly have the ability to enter a diapause (a period of suspended development) during the dry season, for up to five months, during which they do not develop or lay eggs. This usually occurs in the Pomona form which is a lighter colour.

The recent drought has disrupted the breeding cycle of the butterfly’s predators, including the parasitic wasps Ichneumonids. They are long and slender, are often brightly coloured, red, black and white and feed on the eggs and larvae of the butterflies. Many of the wasps have not survived the drought and the reduction in their numbers will influence an increase in the number of a range of butterflies, moths and other creatures that they use to supply their young with food.

Two types emerge

When the Lemon Migrant butterfly goes into the chrysalis stage it can emerge in one of two morph forms that are the same species. The dark morph form is called the Crocale while the lighter morph form is called the Pomona.

There are a number of influences that can determine whether the butterfly emerges as a dark or light butterfly, though the process is not fully understood. The Crocale which develops the dark morph form, generally develops between December and April and has black antenna. The Pomona is the lighter morph form that generally develops between January and September and they have pink antenna, are lighter on top of the wing but are more strongly patterned beneath the wing.

The length of the day can also impact which form emerges, with longer days likely to produce the Crocale form and shorter days producing the Pomona form. If there is an abrupt switch from Crocale to Pomona this may be influenced by rainfall.

Lemon Migrant butterfly, also called the Cassia Butterfly. Photo Kath Vail.

Over 5,000 an hour

Females can lay 700-900 eggs in a lifetime. The eggs are white and vertically ribbed. With the boom of butterflies following the drought there have been up to 5,000 morphs, or butterflies, an hour recorded flying south in southern Queensland in late February. Both forms have been represented and the butterflies have traditionally been recorded as far down as Port Macquarie.

Butterflies evolved 80 to 120 million years ago. Fossils are difficult to find as they are soft bodied creatures.

However, the mythology that surrounds the butterfly can be seen in the stories of the ancient Egyptians who believed that butterflies were the wandering souls of the dead. It appeared to them that during the pupation stage the caterpillar died as it did not move. When it emerged from the chrysalis, they believed that it was dead and then reborn. Butterflies are depicted on their tombs and gravestones as much as 2,500 years ago.

In contrast, the Native American Indian’s legends say that the Great Spirit that created the world meant for his people to love and celebrate the beauties of nature. He loaded the streams with pebbles of every colour, but then he decided they weren’t visible enough, so he called in the South Wind to breathe life into the inanimate pebbles. As the South Wind blew life into the pebbles they suddenly rose and flew gracefully away in a splash of colour. They say these are the first butterflies and moths.

If you are looking for something that not only helps the Lemon Migrant butterflies, but also looks beautiful in your garden, their host plants include the Cassia Brewsteri, Queenslandica, Tomentillia and Senna Aclinis, as well as approximately 20 other Senna varieties.

♦ Thank you to Don P Sands MSc and PhD Honorary scientist from the CSIRO for his assistance with this article. Dr Sands was awarded an Order of Australia for his contributions to entomology, horticulture and conservation .

♦ Kath Vail has been living in the Northern Rivers for 42 years and is passionate about butterflies and dragonflies.

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  1. So nice to read this story. I live in the Hunter Valley and have noticed a lot of these butterflies in my garden over the last few weeks just after the rain. Great to know what they are. Thanks for the informative read.

  2. I have just recorded a lemon migrant butterfly on our property adjacent to the Abercrombie River National Park in the Arkstone area of NSW. This is south west of Oberon and at 800 m elevation. We were very surprised to see it. Beautiful. Thanks for your article.

  3. Thank you for your information on the Lemon Migrant butterfly. We have had a number of them hovering around a Cassia Brewsterii now for two weeks at Moore Creek near Tamworth.

  4. This is an interesting article about Lemon Migrant Butterflies,also called the Cassia Butterfly, and it explains the life cycle of them and what they do in their habitat.Females can lay up to 700 to 900 eggs in a lifetime,the eggs are white and vertically ribbed.Drawings of these butterflies have been seen on tombs and gravestones as far back as 2,500 years ago.

  5. Glad to hear something different to Covid-19
    The plethora of different butterflies around the Noosa beach area since late February are a joy to behold in a world otherwise sadly distracted!
    And particularly when one is old and in self isolation!
    Thankyou for an interesting article!

  6. Really informative and interesting. Thanks for all the info. It was strange to read so much info about Native America and Egypt lore when discussing an Australian butterfly, I thought that was sad.

  7. Cool I live in Nambour Qld and I have been finding lots of caterpillars on my Snowflake bushes/ trees. But was wondering what butterfly or moth had laid the eggs until this morning while giving my plants a drink and found this butterfly on a leaf so I caught it to see what type it was. I then let it go.


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