Life cycle of monarch butterflies

A DigitalNZ Story by Zokoroa

A story about the life-cycle of monarch butterflies and their conservation in NZ.

Butterfly, Monarch butterfly, Insects, Animals, Caterpillars, Flight, Conservation, Life cycle, Lifecycle, Metamorphosis

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. As monarchs are becoming increasingly scarce, each year the Monarch Butterfly New Zealand Trust encourages the public to tag and release monarchs, and to monitor their flight movements. This information is to help record the monarchs' migration patterns and to identify any environmental changes.  

Image: Monarch butterflies

Monarch butterfly (Danaus plexippus) usually seen in backyard gardens & parks between September and March in NZ.

Monarch butterflies

Ministry for Culture and Heritage

Image: Monarch butterfly

Monarch butterfly first recorded in NZ in 1873, having "island-hopped"across Pacific from Nth America. (See Te Ara)

Monarch butterfly

mychillybin

Image: Monarch butterfly , Danaus plexippus.

Monarchs belong to the insect order Lepidoptera (scaly wings). Their Māori name is kākahu, meaning cloak.

Monarch butterfly , Danaus plexippus.

Kete New Plymouth

Spot the difference - female & male 

Image: Female, Monarch Butterfly , Danaus plexippus

Female

Females have thicker black webbing (veins) within their wings, and darker abdomens that are shaped differently.

Female, Monarch Butterfly , Danaus plexippus

Kete New Plymouth

Image: Male Monarch butterfly, Danaus plexippus

Male

Males have two black scent gland spots at the centre of their hindwings to attract female mates.

Male Monarch butterfly, Danaus plexippus

Kete New Plymouth

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. 

Image: Monarch butterfly, Danaus plexippus

Aposematic colouring

The bright orange colours amd distinctive patterns warn predators the butterflies are toxic and bitter-tasting.

Monarch butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch butterfly

Wings are deep orange with black borders & veins. Spots are white along edges. & orange on upper corners of top wing.

Monarch butterfly

mychillybin

Image: swan plants (food for Monarch butterfly)

Main food source is the swan milkweed and balloon plant from the Gomphocarpus genus which was introduced to NZ.

swan plants (food for Monarch butterfly)

mychillybin

Image: Monarch butterfly

Milkweeds contain toxins called cardenolides that monarchs ingest and use as a defense against predators.

Monarch butterfly

mychillybin

Image: Monarch butterfly

Butterflies use their feet to locate and taste nectar.

Monarch butterfly

mychillybin

Image: male Monarch butterfly, Danaus plexippus

The males attract females to mate by releasing chemicals from the two black scent glands on the hind wings.

male Monarch butterfly, Danaus plexippus

Kete New Plymouth

Image: Danaus plexippus, female Monarch Butterfly head

The antennae detect pheromones – odour chemicals – used in courtship.

Danaus plexippus, female Monarch Butterfly head

Kete New Plymouth

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.  (See Monarch Butterfly New Zealand Trust: FAQs)  

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.

Image: Monarch Butterfly laying eggs on leaves and seed pods of swan plant

Females lay 300-400 eggs (c40 per day) on the underside of a milkweed leaf & attach with special glue.

Monarch Butterfly laying eggs on leaves and seed pods of swan plant

Museum of New Zealand Te Papa Tongarewa

Image: Egg of Monarch darkened just before hatching

As the larva develops, the egg changes in colour. It is grey when about to hatch & the black head is visible.

Egg of Monarch darkened just before hatching

Museum of New Zealand Te Papa Tongarewa

Image: Empty egg shell of Monarch eaten by hatched caterpillar

Eclosion (hatching) occurs in 4–8 days. They eat their way out their eggshell & eat the shell which is full of protein.

Empty egg shell of Monarch eaten by hatched caterpillar

Museum of New Zealand Te Papa Tongarewa

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 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.    

Image: Monarch caterpillar

Swan plants contain cardenolides, which is a nutrient inside the plant that helps the caterpillar form a chrysalis.

Monarch caterpillar

mychillybin

Image: Monarch Butterfly, Danaus plexippus

After they emerge, caterpillars start feeding at the base of a leaf so that some of the toxic sap can drain away.

Monarch Butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch Butterfly caterpillar on the stem of a Swan Plant

In 2–3 weeks, the caterpillar grows to about 2,700 times its birth weight!

Monarch Butterfly caterpillar on the stem of a Swan Plant

mychillybin

Spot the head or tail!?

Image: Monarch butterfly caterpillar,Danaus plexippus, Monarch caterpillar

Caterpillars have three distinct body parts: the head, thorax, and abdomen.

Monarch butterfly caterpillar,Danaus plexippus, Monarch caterpillar

Kete New Plymouth

Image: A Monarch butterfly caterpillar , Danaus plexippus

Pair of soft, black filaments (sense organs) at each end of their body. Filaments behind the head wiggle when it feeds.

A Monarch butterfly caterpillar , Danaus plexippus

Kete New Plymouth

Image: Caterpillar of the monarch butterfly,Danaus plexippus

The head has a set of filaments, mouthparts (upper lip, mandibles, & lower lip), & 6 pairs of simple eyes called ocelli.

Caterpillar of the monarch butterfly,Danaus plexippus

Kete New Plymouth

Image: Monarch Butterfly, Danaus plexippus

Each leg has a single claw & the spinneret at bottom of head also produces silk, to help anchor itself to the plant.

Monarch Butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch caterpillar

The maxillary palps (sensory organs below the mandible) help direct food into its jaws.

Monarch caterpillar

Ministry for Culture and Heritage

Image: Monarch Caterpillar

The thorax has 3 pairs of jointed or true legs & the abdomen has 5 pairs of prolegs (false legs) for support at rear.

Monarch Caterpillar

mychillybin

Image: Brown soldier bug

They obtain oxygen through holes in sides of thorax & abdomen called spiracles which connect to air tubes (trachea).

Brown soldier bug

Ministry for Culture and Heritage

Caterpillar moults five times

As the caterpillar grows & 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 University of Minnesota's Monarch Life Cycle.

Image: Mature and young Monarch Caterpillar, New Zealand

As the caterpillar grows & becomes too big for its skin (exo-skeleton), it moults or sheds its skin five times.

Mature and young Monarch Caterpillar, New Zealand

mychillybin

Image: Monarch Caterpillar Hanging Down to Pupate

The larva’s 5th & final moult comes when it weighs c.1.5g & is c55mm long. Stages between moults is called 'instar'.

Monarch Caterpillar Hanging Down to Pupate

Museum of New Zealand Te Papa Tongarewa

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’.  

Image: Monarch Butterfly, Danaus plexippus

Attaches itself upside down in 'J' shape using black silk from spinneret on the bottom of its head to form a silk mat.

Monarch Butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch caterpillar shedding his skin to form a chrysalis

It stabs a stem (called cremaster) from its rear end into the silk pad for it to hang down and form the chrysalis.

Monarch caterpillar shedding his skin to form a chrysalis

mychillybin

Image: chrysalis Danaus plexippus, Monarch Butterfly

Swan plants contain cardenolides, which is a nutrient inside the plant that helps the caterpillar form a chrysalis.

chrysalis Danaus plexippus, Monarch Butterfly

Kete New Plymouth

Image: Monarch Butterfly, Danaus plexippus

A chrysalis is the hard outer case enclosing the caterpillar where the transformation starts into a beautiful butterfly.

Monarch Butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch caterpillar has just shed his skin forming a chrysalis

Chrysalis is a Greek word for gold and describes the gold bands and spots that appear on the pupa.

Monarch caterpillar has just shed his skin forming a chrysalis

mychillybin

Image: Danaus plexippus, Monarch Butterfly

Bodily changes include the straw-like proboscis replacing jaws; and wings & reproductive organs developing.

Danaus plexippus, Monarch Butterfly

Kete New Plymouth

Image: After 23 Days the Chrysalis Darkens, Wings Show Through

The butterfly is ready to hatch when the black, orange, & white wing patterns are visible as pigmentation is completed.

After 23 Days the Chrysalis Darkens, Wings Show Through

Museum of New Zealand Te Papa Tongarewa

4. imago (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.   

Image: Young monarch butterfly just emerged

The butterfly emerges upside down so that gravity can pump fluid from its enlarged abdomen into its wings.

Young monarch butterfly just emerged

mychillybin

Image: Monarch butterfly caterpillar,Danaus plexippus, Monarch caterpillar

The pumped fluid allows the wings to expand and dry so that the monarch can use them to fly.

Monarch butterfly caterpillar,Danaus plexippus, Monarch caterpillar

Kete New Plymouth

Image: Freshly hatched monarch butterfly

Freshly hatched monarch butterfly. The body has 3 major parts: head, thorax, and abdomen.

Freshly hatched monarch butterfly

mychillybin

Image: Monarch butterfly , Danaus plexippus.

The thorax is made up of 3 segments, with second and third segments also having a pair of wings attached to them.

Monarch butterfly , Danaus plexippus.

Kete New Plymouth

Image: Monarch butterfly

Each segment has a pair of legs. As the 2 front legs are tiny & curl against the thorax, it looks like they have 4 only.

Monarch butterfly

mychillybin

Image: Monarch Butterfly, Danaus plexippus

The head has 6 eyes, 2 antennae, 2 palpi (sense organ attached to mouth), & a proboscis (straw-like to sip nectar).

Monarch Butterfly, Danaus plexippus

mychillybin

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.   

Image: Monarch Butterfly

Adult butterflies remain the same size for life. They can fly 80-130 kms in a day & flap their wings 5-12 times a second

Monarch Butterfly

mychillybin

Image: Monarch butterfly on Swan plant

Monarchs start mating after they are three to eight days old.

Monarch butterfly on Swan plant

Kete New Plymouth

Image: Male Danaus plexippus, Monarch Butterfly

After mating & egg-laying, the adult butterflies die & the next cycle of butterflies is continued by their offspring.

Male Danaus plexippus, Monarch Butterfly

Kete New Plymouth

Nectar plants

Garden plants rich in nectar will attract monarch butterflies. Marigold flowers will also help repel aphids from attacking swan plants. Spring flowers, such as Verbena, Cineraria, are ideal for butterflies coming out of overwintering who are very hungry for nectar. (For examples of nectar plants, see: Monty's World and Monarch Butterfly NZ Trust.)  

Image: male Monarch butterfly, Danaus plexippus

Plants rich in nectar include azaleas, blue salvia, dianthus, petunias, sunflowers, wallflowers & zinneas.

male Monarch butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch Butterfly

They use their compound eyes to locate flowers, antennae-like filaments to ‘smell’, & feet to taste the nectar.

Monarch Butterfly

mychillybin

Image: Monarch butterfly on lantana

Monarchs have a long, coiled tongue called a proboscis that it uses to suck up nectar from flowers.

Monarch butterfly on lantana

mychillybin

Image: Monarch Butterfly

Trees that are popular include conifers, bottlebrushes, rhododendrons, cabbage trees, poinsettia, & camellias.

Monarch Butterfly

mychillybin

Image: Monarch butterfly, Danaus plexippus

Fruiting trees & ornamental blossoms (e.g. flowering cherries & mock orange blossom) are also frequented by monarchs.

Monarch butterfly, Danaus plexippus

Kete New Plymouth

Image: Monarch butterfly

Watch the monarch in other people’s gardens and public parks to see what flowers it is nectaring on!

Monarch butterfly

mychillybin

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.)

Image: Monarch Butterfly on Lantana

When air temperature drops to 12.8°C, monarchs tend to flock to milder coastal locations with at least 10°C.

Monarch Butterfly on Lantana

mychillybin

Image: Monarch butterflies

Swarms (known as a kaleidoscope) occur in places like Tauranga Bay in Northland, Hawke’s Bay, Nelson & Christchurch.

Monarch butterflies

Ministry for Culture and Heritage

Image: Danaus plexippus, Monarch Butterfly

Prefer areas sheltered from wind, trees with rough bark surface to cling to, & flowers for nectar are nearby.

Danaus plexippus, Monarch Butterfly

Kete New Plymouth

Threats to the monarch

Insects:

Image: Brown Soldier Bug - Cermatulus nasalis

The brown soldier bug (Cermatulus nasalis) uses its hollow beak as a straw to suck the insides out of larvae.

Brown Soldier Bug - Cermatulus nasalis

Ministry for Culture and Heritage

Image: Preying Mantis,Orthodera novaezealandia

Praying mantids (Miomantis caffra Saussure and Orthodera novaezealandiae Colenso) eat them.

Preying Mantis,Orthodera novaezealandia

Kete New Plymouth

Image: Wasp,Tasmanian paper wasp, Polistes humilis, Australian paper wasp

The Tasmanian paper wasp (Polistes tasmaniensis) picks up larvae and carries them away.

Wasp,Tasmanian paper wasp, Polistes humilis, Australian paper wasp

Kete New Plymouth

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. To help monarchs to locate available swan plants, the Monarch and Milkweed Matchmaking New Zealand Facebook page was set up in 2019. Did you know that a monarch can smell a milkweed from as far away as 2 kilometres! (See Monarch Butterfly New Zealand Trust: FAQs.)  

Image: Swan plant with Monarch caterpillars

As larvae grow they can quickly strip swan plants, leaving hungry caterpillars looking for food

Swan plant with Monarch caterpillars

Kete New Plymouth

Conservation: Monitoring monarchs

Butterfly experts in NZ and the United States are concerned that the number of monarchs have been declining. The National Geographic reported that numbers had plunged more than 80 per cent over the past 20 years in America. The Monarch Butterfly New Zealand Trust encourages member of the public to tag butterflies with a light sticker and identification number provided by the Trust (see Youtube video), and to report sightings. The aim is to gather information about the migration and overwintering habits of monarchs, and the indicators of environmental change. See the Trust's Monarch Sightings Map and online form for reporting sightings.  

Educational resources include:

(This DigitalNZ story was created in April 2019)