Have you found many garden centres and seed sources in NZ get the botanical, common names and descriptions of the swan plant family confused – perpetuating the misunderstanding as to which is which?
I understood the two varieties of milkweed on which the monarch caterpillars thrive best were the swan plant, Asclepias fruticosa and that the larger variety (most commonly referred to as giant swan plant) was A. physocarpa.
Imagine my surprise when emails to Kew Gardens and herbariums in Africa (where many Asclepias species originated from) advised that the names of these two plants had been revised in 2001 – (Goyder, D.J & Nicholas, A. 2001. A revision of Gomphocarpus R. Br. (Apocynaceae: Asclepiadeae). Kew Bulletin 56: 769-836). Dr Siro Masinde, Botanist in Charge of the East African Herbarium in Nairobi, Kenya, confirmed the names and descriptions for me concisely, and I quote:
“The current name for Asclepias fruticosa L. is Gomphocarpus fruticosus (L.) W.T. Aiton. It has five subspecies. This is the one with fruit/follicle that is ovoid, measuring 1.5-2.5 cm in diameter, tapering gradually or abruptly into an attenuate beak.” (i.e. the true Swan Plant).
GIANT SWAN PLANT
“The current name for Asclepias physocarpa (E.Mey) Schltr. is Gomphocarpus physocarpus E. Mey. This is the plant with the larger fruit/follicle that is globose/rounded or subglobose, slightly depressed on one side, not beaked but occasionally somewhat angled at the apex, and very much inflated.”
Similar emails were received from the Herbarium at Kew Gardens, UK, and the Botany Department, Rhodes University, South Africa – the confirmation we required.
This page is also available for download in pdf format: a-beginners-guide-to-nettles.pdf
The New Zealand Red Admiral Butterfly, (Bassaris gonerilla or kahukura), is endemic to New Zealand, which means it is not found naturally anywhere else in the world. In 1928 the Red Admiral butterfly was described as “very common”, but it would probably not be described that way today. A number of reasons have been suggested for its decline such as the parasite wasps Echthromorpha intricatoria that came here from Australia in the 1900s, and Pteromalus puparum, which was deliberately introduced in 1933 to control the Cabbage White Butterfly.
Another possible reason is a reduction in the availability of their food plants. The preferred food plant of the Red Admiral caterpillar is U. ferox (ongaonga or tree nettle). The caterpillars also feed on other nettles such as U. incisa (scrub nettle), U. aspera and U. urens (Dwarf Nettle).
The Nettle family are also host plants for the Yellow Admiral caterpillars. There are many kinds of nettles, with Wikipedia estimating 30-45 species, although not every plant with ‘nettle’ in the name is from the nettle family, Urtica. Nettles have a long history in folklore, with a lot of myths surrounding them as well as a confusing variety of different names for each species. So for example Urtica dioica has also been referred to as U. breweri, U. californica, U. cardiophylla, U. lyalli, U. major, U. procera, U. serra, U. strigosissima, U. trachycarpa, and U. viridis. It is most often called common nettle or stinging nettle, but also goes by the names tall nettle, slender nettle, California nettle, jaggy nettle, burning weed, fire weed and is one of the three different kinds of plant known as bull nettle.
So the following is intended to be a helpful introduction, not an exhaustive list!
Also known as common nettle or stinging nettle. It is a native of Europe, Asia, North America, and North Africa. It is a perennial growing 1 to 2 m high, with leaves 3 to 15 cm long. wikipedia.org, New Zealand Flora
Also known as ongaonga or tree nettle, it is endemic to New Zealand. It is a perennial growing up to 5m high. Ferox is Latin for ‘fierce’ and a hunter once died after pushing through a dense patch of it. wikipedia.org, www.nzpcn.org.nz, Oratia Native Plant Nursery, Flora of New Zealand
Also known as pureora or scrub nettle. It is native to New Zealand and SE Australia. Height variously reported between 40cm and 2m. Leaves 5-12 cm. Likes shade or mild sun and a sheltered spot. wikipedia.org, nzpcn.org.nz, Oratia Native Plant Nursery,
Also known as southern nettle. Native to Chatham and Stewart Islands. It grows up to 1m tall with dark green leaves, 10-15 cm by 8-14cm. nzpcn.org.nz, Oratia Native Plant Nursery, Flora of New Zealand
(Occasionally referred to as Urtica debilis) Also known as New Zealand pellitory although it is found throughout the Southern Hemisphere. A spreading annual plant forming patches up to 50cm diameter. It has the advantage over other Admiral host plants of not having a sting, however its small leaves make it less than ideal. wikipedia.org, nzpcn.org.nz, Oratia Native Plant Nursery, Flora of New Zealand
Children and Nettles
Unfortunately nettles are listed in “Safety in pre-school centres: plants to avoid”
so simply planting them in your children’s butterfly garden is a no-no if you are a pre-school. However there are still a number of options for making Red and Yellow admirals part of a butterfly garden for children.
The easiest option is stick to the stingless Parietaria debilis and accept that it will not be able to support many caterpillars. Another option would be to plant the nettles behind a fence or barrier so the children can see them but can’t touch. Alternatively grow the nettles in hanging baskets out of their reach. Perhaps combine those options by placing Parietaria debilis where they can have a close look, but have the main supply of nettles elsewhere. For a butterfly garden in a home another option is to accept that a nettle sting is something they will get over, and they will treat nettles with more caution in future.
Phenology and parasitism of the red admiral butterfly Bassaris gonerilla. New Zealand Journal of Ecology (2004) 28(1): 105-111, downloaded from http://www.nzes.org.nz/nzje/free_issues/NZJEcol28_1_105.pdf
Moore, L.B.; Edgar, E. (1970) Flora of New Zealand. First electronic edition, Landcare Research, June 2004. Transcr. A.D. Wilton and I.M.L. Andres. http://FloraSeries.LandcareResearch.co.nz.
An account of a 60-year-old hunter being affected by Urtica ferox was reported in the NZ Medical Journal 106, No. 957 on 9 June 1993.
I have uploaded the full pdf to our website. You can read it here: d9773enz.
More than ever before monarchs need our help. As well as the shocking statistics coming from North America, where deforestation, pesticide use, GM crops and climate change are affecting the migration, the monarchs are suffering here. In this country they have been ravaged over the last two seasons by wasps, their major predator. Warm winters here in 2013 and 2014 have meant more social wasps. Hopefully this past winter has been colder and their numbers have been reduced; if this is so, there will be more hungry monarch caterpillars than ever.
The relationship between monarchs and milkweed (such as swan plants) is fascinating. Consider the predators, parasites and pathogens that affect monarchs. If people loved swan plants as they do rose-bushes, then we would see the monarch as a pest!
It is not a simple exercise for a commercial operation to grow swan plants. The plants need to be in a good condition when they go on sale. The two main challenges are monarchs and aphids. After all garden centres won’t want to sell plants that are covered with aphids or are bereft of leaves.
Some growers resort to using pesticides. Hopefully they don’t release their plants for sale until the chemicals are no longer active.
A female monarch lays on average of 700 eggs (one was recorded as laying 1179 eggs). After the caterpillar emerges from its egg it will grow almost 3000 times in size over the following two weeks. So one day you have lots of leaves, a week later and the plants can just be leafless stalks.
If you grow your own plants from seed you will know for certain that the leaves are safe for caterpillars. We encourage everyone to hold plants over from previous years. When a plant is over 1.5 metres in height, and if it is well fertilised and kept healthy, the growth in the spring and summer will almost keep up with the caterpillars.
So if you haven’t bought your plants this year, get twice as many and protect some for next year’s monarchs. Also get some seed – Yates gives the MBNZT a donation for each packet sold – and grow more plants. If seedlings sprout up in inconvenient places leave them until you need food. Pull out the plant, or cut it off at the stem and put it in a bucket of water, splitting the bottom of the stem before you do so it will better absorb water.
Here are some more tips to help you raise your Monarchs so that they become beautiful butterflies.
Between egg and chrysalis the caterpillar or larva is going to shed its skin five times. When they are shedding their skin it is important not to disturb them. We suggest that you observe the life cycle but do not touch or interfere. Monarchs have been undergoing metamorphosis for hundreds of years and do not usually need our help.
If your larvae need more food we suggest you let them move themselves to the new plant. A potted plant can be placed next to an existing plant. Or, if the existing plant has no leaves, then prune it and put the stems you have cut off (with caterpillars) at the base of the new plant.
By the way, milkweed and Monarchs are poisonous so be careful when handling them. There is more information about this HERE. Monarch larvae store toxic steroids (known as cardenolides) from the milkweed they eat and use these cardenolides as a defence against predators such as birds. The bad taste and toxicity of both the larvae and adults are advertised by their warning colour. When a bird predator tastes a Monarch it learns to associate their colour and pattern with the bad taste and avoids preying on them in the future. (Interestingly, the Shining Cuckoo is not affected and will eat them.)
Be aware that there are different types of milkweed and the new plant(s) may not immediately appeal to your larvae. Water the plant well so that if there is an imbalance of cardenolides, they will be diluted.
If you are buying new plants as food for your caterpillars you should be careful about buying plants that have pesticide spray residue on them as this will affect and may even kill your brood. Ask your supplier if they are spray-free – or better yet have a go at planting next year’s in advance from seed. Seed is available on our website HERE.
Pesticides include fly sprays, plug-in insect controls and flea collars on pets so bear this in mind if you bring your larvae indoors.
If you are concerned that your caterpillars are dying, we suggest that you look in the forum HERE to see if there have been other similar reports – or add your own post. Don’t forget to add details like your locality, if the plants or new or well-established, number of caterpillars affected, if you have neighbours who spray and anything else you think is relevant.