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By Kennedy Harris (kennedyh)
(Editor's Note: This article was originally published on November 16, 2007. Your comments are welcome, but please be aware that authors of previously published articles may not be able to promptly respond to new questions or comments.) I have for a long time known that the Scrub Nettle Urtica incisa is the food plant for the caterpillars of the Australian Admiral butterfly (Vanessa itea). This means that almost every time I pass any nettles, I give them a quick once over for caterpillars. I have done this for some years without success, but on 31 August 2006, I did find a lot of caterpillars feeding on the nettles in Morwell National Park in Victoria, Australia. I knew at once that they were not Australian Admirals, but I had no idea what they were (or would become). Here is the very hairy caterpillar that I found. I decided to see if I could rear the caterpillars and thus find out which moth they would become, so I took two caterpillars home and put them in a jar with several stems of stinging nettles. The caterpillars fed avidly on the nettles, but the nettles of course wilted fairly quickly in the jar and I had to collect more nettles after 3 days. I kept collecting stinging nettles every 3 days for most of a month. Not a simple matter and very few changes of nettle occurred without my getting a few stings along the way.
The caterpillars grew and changed in appearance, so that on 18 September, after 18 days, they looked like this. As they grew nearer to pupating, I had to make a guess as to where they would like to pupate. I had a suspicion that they were a Tiger Moth of the genus Spilosoma and that led me to suspect that they would pupate among leaf and bark litter on the ground. I therefore provided a layer of dead leaves, bark and twigs in the bottom of the jar. At about the end of September they completed their caterpillar phase and both weaved a cocoon, incorporating the hairs from their final caterpillar stage and in this cocoon became a chrysalis or pupa. Here is one of the cocoons with all the bark and leaves incorporated into it. At this stage I removed the remnants of the nettles and placed three or four twigs in the jar, so that if a moth emerged it would have something to perch on. I then kept the jar in a spot where I would look at it every day so that I would not miss the emergence of the moth.
It was not until 15 February 2007 that I was delighted to find that one of the moths had emerged, 5½ months after I first found the caterpillar, and what a beautiful moth it proved to be. I was right in guessing it to be a Tiger Moth in the genus Spilosoma. It proves to be the Black and White Tiger Moth Spilosoma glatignyi, but all the references I could find, listed a lot of food plants for this moth, but none mentioned stinging nettles. In Morwell National Park, the scrub nettle is an important food plant for this moth, after seeing the caterpillars once, I found them on almost every patch of nettles in the park and there are plenty of them as the Friends of the Park well know (some from bitter experience). While I was rearing these caterpillars, I continued to look at every patch of nettles, seeing a lot more of the same caterpillars, but on 19 September, I finally found the caterpillar I had been searching for, an Australian Admiral butterfly's caterpillar. It looked a pretty well-developed caterpillar and it was on the stem of a nettle, very near the top. I thought I would put it in the jar with the other caterpillars (to share their nettles), but I kept it in a plastic bag overnight, so that I could take some more pictures, before adding it to the jar. When I went to get it the next morning, I found the caterpillar curled back on itself and firmly attached to the plastic bag. I thought it had started to pupate, so I left it in the plastic bag and by the evening when I next looked it had formed itself into this lovely chrysalis, which was firmly attached to the plastic bag. In order to support the chrysalis, I had to cut a piece out of the plastic bag and wrap it round a piece of garden stake, using sticky tape to fix it in place. I kept the stick with the chrysalis on it free standing in our family room and I did not have to wait 5½ months for this one to emerge; after only 2 weeks Fay told me there was a butterfly flying around the room. Sure enough, the chrysalis was empty and I found a beautiful Australian Admiral butterfly perched on the curtain. I didn't try and photograph the butterfly, I simply let it free in the garden, but here is a picture of an Australian Admiral that I took recently. So next time you collect a few stings from the nettles, remember that there is a beautiful moth and a beautiful butterfly depending on them for food and so they make a very positive contribution to our park. It is not just in Australia, that stinging nettles are hosts to beautiful butterflies. In Europe and America, the Red Admiral butterfly Vanessa atalanta also chooses stinging nettles as its favourite plant for rearing its caterpillars. In New Zealand too, the New Zealand Red Admiral Vanessa gonerilla chooses one of the fiercest of nettles, the Tree Nettle Urtica ferox for its caterpillars. There is a good side to Stinging Nettles wherever they are found!
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