The Universal Monarch

The following essay was written by the late R W Mayson, of Grey Street, Wanganui in 1983. A retired school principal, he wrote to my son, aged 9, a kind, friendly and informative letter, and it was accompanied by this background information on the Monarch. Some of the points he makes are now disputed by scientific evidence, but we publish the report as Mr Mayson wrote it.

Jacqui Knight


There are few things more beautiful in a garden than the Monarch Butterfly lazily flaunting its colours. And anyone can have them, all that is needed is one or more Swan plants in a sunny corner.

The Swan plant is so called in New Zealand, because the green seed pods shaped like a swan, the stem being the long neck. Years ago it was popular with children for inclusion among the decorations of their water-bowls. The more common name is Milkweed, the sap being milky-white. In some countries it is also called the cotton­weed because the inside of the ripe pod is not unlike a cotton ball, each seed being attached to a white feathery filament. This, presumably is to aid the dispersation of the seed by the wind. The plant is a native of America, but has been spread around the world.

It is not known how it reached NZ, though possibly some seeds were in straw or similar material used for packing goods imported from overseas, or it could have been brought in deliberately. It has not spread as a weed in NZ, and appears to exist only as a cultivated plant. When the Monarch arrived, its host plant was waiting for it.

The Monarch provides one of the romances of natural history. It spread from South America near the River Amazon, into North America, even as far as the Arctic snows; eastwards to Bermuda, and reached England, France and Spain, though it has never established itself in England. Others spread westwards across the Pacific, reaching Queensland in 1870, and Melbourne in 1872. The spread continued-through the Malayan Archipelago, and may have met up with the eastward flight, thus encircling the world.

It is not known definitely when it reached NZ but there is talk of them being sighted in Auckland at the beginning of this century. Apparently, though, it is only comparatively recently that it has been established itself here. And new arrivals come across the Tasman each year.

Fortunately the host plant is of no economic importance, and the spread of this magnificent butterfly ’causes no trouble to man. It flourishes in its new homelands, as its natural enemies have’ evidently been left behind, and it is immune from attacks by birds possibly because it has an objectionable taste. It quietly flits and glides about, for there is no reason for it to hurry or hide. Many insects that are distasteful to their enemies are brightly coloured as if to advertise that they are better left alone.

The butterfly multiplies rapidly, with three generations in a normal year. The larva (caterpillar) grows to a large size and consumes a lot of foliage in its lifetime. As the only host plants are those raised in gardens, and often only one or two at a time, we have witnessed an interesting phenomenon over the last several years.

Firstly the butterfly multiplied until it outgrew its food supply.

Not only were all the leaves and soft stems eaten, but also the flowers and the young seed pods, so that the plant disappeared in some places. In the next years, of course, there was little food for the larvae of the increased butterfly population, and fewer specimens developed to maturity. This gave the plants, or some of them, a chance to recover, over the next period. And so the cycle goes on. One Wanganui enthusiast protects some of his plants by growing them in a shelter covered with netting, to ensure a continuous supply of seed, and reports that he has requests for seeds and plants from many parts of NZ, from the Bay of Plenty to Christchurch. This year (1983) there have been fewer butterflies about, and even the unprotected plants are carrying seed pods. This may be due to the cycle mentioned above, or to the very poor summer we have had, or to both.

The Monarch belongs to the Order of insects called Lepidoptera, (scaly winged). The wings are covered with tiny scales of differing colours to give us the patterns we see. Lepidoptera are classified under two main sub-orders, butterflies and moths, and the main difference separating the two is the shape of the antennae (feelers).

The butterfly’s are clavate (club like), and the moth’s pectinate (feathery). When they rest, the butterfly holds its wings over its back, exposing its body, whereas most moths rest with their wings folded over their bodies. Butterflies fly by day, and most moths by night. A common exception to this is the black and white Magpie Moth, the larvae of which are so fond of Cinerarias.

In their lifetime, Lepidoptera undergo what is called a complete metamorphosis. That means that in their life cycle there are four distinct stages: the egg, larva (caterpillar), pupa (chrysalis),  and imago (adult).

One can often see the female Monarch laying its small creamy-white eggs on the underside of a leaf of the milkweed. After a short while the egg darkens and the small larva emerges to begin feeding at once, choosing the most tender part of the plant, the new small leaves on the growing points of the bush. The larval stage is the period of growth. Although the adult feeds on nectar from flowers, it seeks only sugars to maintain its strength for flying. It does not grow or change in any way. Since it grows only in the larval stage, it is then that it has a prodibious appetite, and increases in size rapidly. The method of growth is interesting. We vertebrates v have an inner skeleton. The bones grow longer and stronger in keeping with the rest of the body. The insect has what is called an exo-skeleton, or integument, an outer covering made up of plates of chitin, which are very hard. They are held together by tissues which, in the larval stage can stretch to a limited extent. When the larva grows so that the chitinous exo-skeleton is fully distended the outer covering splits and the second instar emerges in a new loose ‘dress’ which is tailored to allow for growth. But this too becomes too small and the process is repeated. This happens several times. At the end of the last growing period of the larva all is ready for the third stage, its life as a pupa, to begin. The full grown larva fastens itself to a leaf, twig, or any other handy site, head downwards, by a short but strong black silken thread, and hangs downwards in the shape of a hook. Wonderful changes take place in the body, where the pupa is being formed. When all is ready, the larval skin is sloughed off, and the exquisite green pupa, ornamented with gold spots, hangs head downwards from the black thread. Inside all the organs have turned into a milky substance, and from buds, the complete adult will grow. Indeed the growth begins before the pupa emerges, for many of the external parts of the adult insect can be seen in the shape of the pupa.

The fourth stage, the emergence of the adult butterfly, is preceded by the pupa turning dark, and the colour of the wings being faintly visible through the pupal case. The emergence is a fascinating sight. The pupal case splits and the butterfly emerges. The wings are small at first, increase in size, going through a rumpled stage to perfection. Inside the wings are veins, plainly see in clear­winged insects such as the dragon-fly and the bee. These veins are tiny tubes, and fluid is pumped from the body of the insect, along these tubes, causing the wings to become distended. Between the veins, the upper and lower surfaces of the wings come together and harden. After an hour or two, when the wings are fully extended and dry, the butterfly will flex them for several minutes, and then take off.

The venation of the wing, that is the pattern of the veins, is constant in each specie, and is used by entomologists for classification purposes.

The Monarch is one of the few butterflies that is truly migratory, at least in its homeland. The migrations are observed regularly, going north in the spring from its hibernation near the Mexican border, as far as Canada. In the Autumn they congregate like swallows and gradually move southwards in an ever-growing army of tens of thousands. They fly from 200 to 300 feet above the ground and when they settle at night, they appear to change the colour of the vegetation. They over-winter near the border with Mexico in a state of semi-hibernation.

In the home garden the larvae are inclined to wander. The fully ­grown larvae will sometimes wander before pupating, and pupae will be found in many situations. If it is possible to remove a pupa carefully without handling it, it can be taken inside where the emergence of the butterfly can be observed. – Remove a portion of the object to which it is fastened. Fasten this firmly to a twig with cotton so that it hangs freely. The twig can be put in a vase which can be placed anywhere, but a windowsill is a good place. With any luck and close observation, all the family can watch the emergence.

Milkweed can be grown easily from seed. Ensure that the bed does not dry out over quite a long germination period – up to three weeks or a month. It is wise to wait until there is a good root formation before transplanting, until the second or even the third set of true leaves appear. But the plants are easy to grow. Most weeds are! But even though a weed, the plants will respond to compost and fertiliser. A light dressing of nitrogen will work wonders. The plants grow up to six feet (two metres tall if allowed to, and will fit into most situations. They usually do not bear seeds until the second year

The only common disease is a form of collar rot. It is better not to heap up the soil around the crown, and care must be taken not to damage the stems when hoeing the garden.