Monarch butterflies can usually be seen flying amongst the flowers in backyard gardens and parks between September and March in New Zealand. They have an important role to play in helping to pollinate many flowering plants. Each of us can also have a role to play to ensure that the monarch butterfly thrives in our gardens, parks and suburban areas, along with other butterflies and moths. The Moths and Butterflies of New Zealand Trust was formed in 2005, to provide butterfly-friendly conservation advice on ideal spaces, flowers and trees.

Spot the difference - female & male 

Distinctive features

The large and brilliantly-coloured monarch butterfly is among the most easily recognizable of the butterfly species. The wings are covered with tiny scales of differing colours to give us the patterns we see. Monarch butterflies communicate with colours and scents. They signal to other animals that they are poisonous by having bright orange wings. The males attract females to mate by releasing chemicals from scent glands on the hindwings. 

Life-cycle

Monarch butterflies go through four stages:  the egg, the larva (caterpillar), the pupa (chrysalis), and the imago (adult butterfly). During mid-summer, the process goes from egg to adult in about 23 days. A butterfly on 28 February may come from eggs laid before 5 February – but very unlikely to be from an egg laid after that date. Once adults, monarchs have an average lifespan of six to eight weeks in the summer, and 6–8 months if the butterfly pupates in winter. There can be up to three generations of monarch butterflies born each year.  

1.  Egg: 4-10 days to hatch 

The monarch butterfly lays eggs on milkweed plants. It takes about 4-10 days for the eggs to hatch into a caterpillar. Times are longer for cooler conditions, than in the peak of the summer.

Spot the head or tail!

 2.  Larva stage (caterpillar): 9-20 days to grow 

The baby caterpillar spends its time eating plants in order to grow. In 2–3 weeks, the caterpillar grows to about 2,700 times its birth weight!  (See Science Learning Hub)  

Main food: Swan milkweed and balloon plant

The main food source for caterpillars (larvae) comes from the Gomphocarpus genus, which includes the swan milkweed and balloon plant. The Swan plant is so called in NZ, because the green seed pods are shaped like a swan - the stem being the long neck, and the sap is milky-white. Adult monarchs also feed on the nectar of milkweed flowers, as well as other plants.     

Caterpillar moults five times

As the caterpillar grows and becomes too big for its skin (exo-skeleton), it moults or sheds its skin five times. For photographs and a description of how the caterpillar looks after each of the five stages of moulting (known as instar stages), see Monarch Joint Venture - Life Cycle.

3. Pupa stage (Chrysalis): 10-28 days to metamorphosize

After the caterpillar is fully-grown, it will find a sheltered place to attach itself in an upside down 'J' shape. It will then start the process of transforming into a chrysalis over the next 10-28 days. The monarch’s scientific name, Danaus plexippus, means ‘sleepy transformation’.  

4. Imago stage (adult): Butterfly emerges

The monarch butterfly will emerge hanging upside down from the pupa with an enlarged abdomen that is full of fluid. By hanging downwards, gravity will help them to pump the fluid from their abdomen into their wings. This allows the wings to expand and dry so that the monarch can use them to fly.   

Adult MONARCH BUTTERFLY: LIVES FOR 2-8 MONTHS

The adult butterfly has an average lifespan of six to eight weeks if it pupates during the summer, but this extends to 6–8 months if the butterfly pupates in winter. The primary role of the adult stage is for the monarchs to reproduce — to mate and lay the eggs that will become the next generation, with three generations occurring each year.   

Conservation of monarchs

Swan plants, nectar plants & trees

The main food source for monarchs are the Swan Plant (Gomphocarpus fruticosus), Giant Swan Plant (Asclepias physocarpus) and Tropical Milkweed - Bloodflower (Asclepias curassavica). Garden plants rich in nectar will also attract monarch butterflies. Spring flowers, such as Verbena, Cineraria, are ideal for butterflies coming out of overwintering who are very hungry for nectar. For advice on growing plants and which plants to avoid, see Moths and Butterflies of New Zealand Trust – Monarch Health. 

Winter months 

Monarchs are more sensitive to cold than other butterflies and are less common in the far south of NZ. When the air temperature drops to 12.8°C around April or May, monarchs start flocking to sites that tend to be in milder coastal locations where the temperature remains at least 10°C. When the temperatures warm up in Spring (around September/October), butterflies move inland to  reproduce. (See Science Learning Hub and The Butterfly Musketeers.) For tips on maintaining swan plants in gardens over winter whilst awaiting the return of the monarch butterflies, see Moths and Butterflies of New Zealand Trust.

Threats to the monarch

Insects:

Lack of swan plant food:

The monarch butterfly's main habitat is urban and suburban gardens. Swan plants are the main source of food. However, as larvae grow they can quickly strip the plants, leaving hungry caterpillars looking for food. Did you know that a monarch can smell a milkweed from as far away as 2 kilometres! (See  Moths and Butterflies of New Zealand Trust)   

Monarch butterflies also face competition for the swan plant from aphids: "By piercing the cell wall of leaves and stems to suck the sap they weaken the plant, leaving a wound that can allow disease to get in".  (Source: Moths and Butterflies of New Zealand Trust which provides advice on dealing with aphids.) Planting marigold flowers near swan plants will also help to repel aphids - marigolds emit a scent unattractive to aphids and attracts hoverflies, which are a predator of aphids. 

Monitoring monarchs

Butterfly experts in the United States and NZ are concerned that the number of monarchs have been declining. 

Every autumn millions of monarchs leave southern Canada and northern United States to journey 5,000 kilometres southwards. After spending the winter in the Mexican mountains, they return northwards breeding along the way. Their offspring then make the trip back to Mexico at the end of the following summer. The National Geographic (22 Dec 2018) reported that numbers had plunged more than 80 per cent over the past 20 years in America. In 2022, the International Union for the Conservation of Nature added the monarch butterfly to its "red list" of threatened species and categorised it as "endangered" — two steps from being extinct. (Source: NZ Herald (23 July 2022), “Monarch butterflies now listed as endangered”)

In NZ, the tagging of monarch butterflies began in 2005/2006 as a trial and continued until 2021. The aim was to gather information about the migration and overwintering habits of monarchs, and the indicators of environmental change.  Based on the data that was reported, there appeared to be no discernible pattern of migration or any common destination.  See Moths and Butterflies of New Zealand Trust and the Science Learning Hub.  

During 2020-2021, an outreach science programme was conducted by Victoria University for citizen scientists to help examine diseases in monarch butterflies caused by parasites. The protozoan parasite Ophryocystis elektroscirrha, or OE, causes adult butterflies to have crumpled and deformed wings. Members of the public were asked to forward samples of spores collected by pressing a bit of cellotape against the butterfly's abdomen. The findings showed there was more OE in the warmer north and less in the south. See: Victoria University of Wellington, Wellington Faculty of Science - Outreach Programme “Tracking Disease in New Zealand's Monarch Butterflies looking a diseases”   

FIND OUT MORE - Educational resources include:

• Moths and Butterflies of New Zealand Trust
• The Butterfly Musketeers
• Science Learning Hub
• Also see images on DigitalNZ  from content partner iNaturalist NZ -  Mātaki Taiao