CanterburyNature

Danaus plexippus

Written by Joanna Hodgson (Lincoln University)

July 2005

Edited by Michael Hudson, Lincoln University, September 2006

Taxonomy

• Scientific name: Danaus plexippus (Linnaeus, 1758)
• Popular Common names: Monarch butterfly, kakahu
• Other common names: wanderer (Australia), milkweed Butterfly (Britain), black-veined brown

• Kingdom: Animalia
• Phylum: Arthropoda
• Class: Insecta (the birds)
• Order: Lepidoptera (the butterflies and moths)
• Family: Nymphalidae

• New Zealand Status: naturalised

• Taxonomy sources: Gibbs & Lessiter (1994); Braby (2004).

Identification

Species Description

The monarch butterfly (Danaus plexippus) is frequently seen in most parts of New Zealand. Easily identified by its bright colours the monarch butterfly has a large wingspan commonly between 80-100 mm (O’Brein, 1985). The wings have a deep orange-brown colour on the upper side with orange spots at the apex of the forewings. Prominent white spots are found on the black wing border and distinguishing black veins run throughout both wings (Gaskin, 1966). Through close observation thick black and white scales and hairs covering the head of the butterfly can be seen. Although having six, hairy, long spreading legs there appear to only be four as the first pair are reduced in length and tucked up tightly against the thorax. At the end of the legs there is a large hook like claw which is used to attach and steady the butterfly on vegetation (Gibbs and Lessiter, 1994). To identify between the male and female there are two distinguishing factors. Firstly the black on the males wings is thinner than those on the females. Secondly, located under the middle of the hind-wings of the male is a tuft of scales which cover a scent pouch (Egmont and Kirby, 1896)

Similar species

The monarch butterfly is fairly unique in New Zealand and easily identified by most. However the rare lesser wanderer (Danaus chrysippus), which is a straggler from Australia, can be mistaken for the monarch. Both butterflies have similar features such as a broad back and a black wing margin dotted with white spots. However, the lesser wanderer has a much smaller wingspan of 70 mm and does not have strong black lines across the wing (Gibbs and Lessiter, 1994)

Geographic Distribution

Full natural and naturalised range

The species D. plexippus originally came from North America. As well as introductions by humans the monarch’s strong migration ability has allowed it to naturally colonize large areas of the world, probably including Australia and New Zealand (O’Brien, 1985). It is also present in most of the islands in southwest Pacific, Central and South America, West Indies, Galapagos Islands, New Guinea, Solomon Islands westward to the Moluccas and North to the Phillippines. Taiwan, Mauritius, India, the Azores, Madeira, Canary islands, southern Portugal, southern Spain and are occasionally found in the United Kingdom, Ireland and southern France (Egmont and Kirby, 1896).

New Zealand range

Monarchs are widely spread through most parts of New Zealand. They are most commonly found in the North Island because of the preferred warmer temperatures. Monarchs are also spread through the lowlands of the South Island; with exception of the far southern areas where they are seldom found (O’Brien, 1985).

Canterbury range

Monarch butterflies occur naturally in Canterbury and can be found during warmer periods throughout Canterbury gardens (personal observation).

Natural History in Canterbury

Habitats

The natural habitat of the monarch butterfly is in the lowland areas of New Zealand in warm to hot locations. The monarch larvae are dependent on the garden shrub ‘swan plant’ (Asclepias fruticosa) which does not grow naturally in New Zealand. Because of this monarchs, to a high degree, have become a garden insect in New Zealand (O’Brien, 1985).

Preferred habitats

The monarchs preferred habitat is where there are large quantities of sun and heat. Because of this the main distribution in New Zealand is on the North Island. Less affected by strong cool winds, lowland areas are preferred. As previously mentioned the monarch is restricted to areas such as gardens where swan plants are close by to feed on (Laidlaw, 1970).

Phenology/Breeding

Monarchs breed over a large geographic and temporal range. They lay eggs on swan plants, utilizing the majority of the 100 North American swan plant species. The reason for this is to ensure a ready food supply for the larvae upon hatching. The average wild, female monarch is estimated to lay 300 to 400 eggs during her lifetime; captive monarchs lay an estimated 700. Eggs hatch within four days of being laid; however the rate of development is dependent on temperature. Summer-generation monarchs first mate between the ages 3-8 months and begin to lay eggs immediately after they first mate. Over winter monarchs do not lay eggs until spring. The eggs and larvae only have a small chance of reaching adult hood with studies by Borkinet al. (1982) documenting mortality rates of over 90% during the egg and larvae stages (Oberhauser and Solensky, 2004).

Life cycle

The lifecycle of the monarch is complicated with several stages that involve the transformation of the exoskeleton through the process called moulting. Moulting in the monarch consists of several stages from the tiny egg, through five stages of larval (or caterpillar) growth to a pupa and eventually through to an adult monarch. Together the growth process takes just over a month to complete in mid summer and longer at other times of the year. The life cycle begins with the laying of small creamy-yellow eggs which hatch after 3-4 days into larva (the larva are often called a caterpillar). The larval form consists of a rigid head capsule at the beginning of a long soft-skinned body which has eight pairs of legs. There are five larval stages which are measured by the size of growth. On reaching a length of around 55mm and a weight of 1.5g the larva stops eating and finds a secure place to hang upside down in a ‘J’ position. Staying this way for a day the larva changes into a pre-pupa. The pre-pupa then undergoes shedding of the larval skin exposing a jade green monarch pupa (sometimes called chrysalis). In the final stage it swallows air and pumps the fluid into areas where expansion is required. The small pupal case splits and the monarch is released (Gibbs and Lessiter, 1994).

Longevity

The lifespan of an adult monarch is difficult to measure but is estimated to be 60-70 days. During this time 30 days are spent migrating and the remaining 30-40 days reproducing. However the lifespan can become as long as 6-7 months if the butterfly is born in autumn. This occurs over winter when hibernation takes place slowing down body functions (Gibbs and Lessiter, 1994)

Dispersal

Monarchs are graceful flyers who, in a sense, float around gardens from plant to plant (personal observation), however during migration their flight is strong and capable taking them large distances; in-fact as far as 2000 km in 2-4 days (Brownlie, 2002).

Diet

The monarch larva diet consists of milkweed plants. These are the only food the monarch larva feed on in the wild. Swan plants belong to the family ‘milkweeds’. There are four different species of milk weed that grow in New Zealand; Gomphocarpus fruticosa, Gomphocarpus physocarpa, Asclepias curassavica and Asclepias tuberose. The adult monarch feeds on the nectar of flowers. Once the monarch has landed on a flower, the detection of nectar is through its feet. Once detected the monarch uses its long tubular tongue (proboscis) to suck up the juicy, sweet nectar (Gibbs and Lessiter,1994).

Behaviour

Monarch butterflies, unlike any others, assemble in large groups over the winter period and in North America undergo significant migrations. In New Zealand the butterfly swarm is mostly in-active during this time, but not totally dormant. When the warm sun appears so do the monarchs; ready to soak in the heat and search for winter nectar. After each storm the monarch numbers are reduced. At the end of June, as the temperature rises above 10 degrees, most butterflies have left the winter sites; a few remain until September (Gibbs and Lessiter,1994).

Predators

Butterflies are under continuous threat from predators during their life cycle. Insect eating birds are in constant search for a vulnerable insect; counter evolution of the monarchs has seen the adaption of a warning coloration to protect themselves (Oberhauser and Solensky, 2004). The chemicals (alkaloids) they receive from the swan plant are toxic to other animals. The alkaloids of the swan plant affect the heartbeat of animals and often result in vomiting. Predators become aware of the monarchs distinctive warning colouration. However, this does not protect them from insect predators such as the flat, brown soldier bug (Cermatulus nasalis). The soldier bug feeds on the monarch larva by spearing the caterpillar with its long beak and sucking out the contents (Gibbs and Lessiter, 1994).

Mutualisms

Butterflies are an important pollinator. The monarch is attracted to brightly coloured flower from which they receive nectar. At the same time they involuntarily pick up sticky pollen which is then transferred to the next flower it lands on. In this way pollen is spread around the garden (Gibbs and Lessiter, 1994). Both the monarch and the flowering plants have a mutualism where the butterfly receives food from the flower, in return the flower is pollinated.

How to find the Monarch butterfly

Adult monarchs can be found during the summer periods in local gardens where there are plenty of flowering plants as a food source and swan plants close by to lay eggs on. They frequently over-winter in large colonies in large trees, for example in parks of Christchurch City, and can be seen flying about on unseasonably warm winter days.

Abundance and Conservation Status

• New Zealand: abundant
• Canterbury: moderately abundant

The monarch butterfly is abundant throughout New Zealand, especially in warmer areas such as in the North Island. Because Canterbury has a cooler climate, the monarch is less abundant.

Significance for people

Modern Uses

Monarch butterflies are a beautiful and interesting creature to have in the garden. In addition they are reliable pollinators. Often people plant swan plants in there garden to attract them into there landscape, which make for a garden environment full of life.

Summary

Monarch butterflies are an important part of the New Zealand landscape. A well as being a beautiful attribute to the local garden the monarch is an asset to the plant community as a pollinator. Monarchs are wide spread around the world with a strong flight and migrating ability. They have adapted well to the New Zealand environment and are under no threat due to the use of alkaloids and warning colouration. In my opinion, monarchs are without a doubt New Zealand's most beautiful butterfly.

References

Brownlie, B. (2002). Life cycle of the monarch butterfly. Scholastic, [unknown].

Egmont, W. & Kirby, M.D. (1896). Butterflies and moths of the United Kingdom. George Routledge & Sons LTD, London.

Gaskin, D.E. (1966). The butterflies and common moths of New Zealand. Whotcomb & Tombs LTD, New Zealand, Australia, London

Gibbs, G. & Lessiter, M. (1994). The monarch butterfly. Reed Books, Auckland, New Zealand.

Oberhauser, K.S. & Michelle, J. (2004). The Monarch Butterfly, biology and conservation. Cornell Univesity Press.

O’Brien, C. (1985). Butterflies and Moths. Reed Methuen Publishers Ltd. Auckland, New Zealand.

Laidlaw, W. B. R. (1970). Butterflies of New Zealand. Collins Bros and co, Auckland, New Zealand.

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