Australia & New Zealand
Family - NYMPHALIDAE
subfamily - DANAINAE
Tribe - DANAINI
subtribe - DANAINA
The subfamily Danainae, which includes the
Monarchs & Tigers, Nymphs and Crows, comprises of about 190 species
butterflies in this subfamily are thought to be toxic or distasteful
to avian predators. Their bodies contain toxins derived from the
larval foodplants, often supplemented by further toxins derived from
pyrrolizidine alkaloids in adult food sources.
This form of defence is called Batesian mimicry. It is only
effective because the toxic species far outnumber the non-toxic
species. If the situation was reversed, and most of the butterflies
attacked were palatable, the mimicry would serve no purpose.
Monarchs and Tigers belong to the genus
Danaus. They are large butterflies,
characterised by their orange wings, which have a black apex, and
white subapical spots. On the males there is a patch of raised
androconial scales on the hindwings.
The bright colours
advertise their poisonous qualities
to birds in the same way that the bands of yellow and black of wasps
advertise the fact that they can sting. Any bird that attempts to
eat the butterfly will immediately vomit and suffer nausea and other
side effects. Birds have excellent memories and an ability to learn
from unpleasant experiences, so consequently avoid eating similarly
coloured butterflies in the future.
The Monarch is the
most famous migrant in the butterfly world. Its
powers of migration are so great that it has been able to spread to
across the Americas from Canada to Peru. It has also crossed the
Pacific ocean, reaching Australia, New Zealand and Papua New Guinea;
and across the Atlantic to north Africa, southern Europe and even to
Danaus plexippus, New Zealand,
© Rob Herd
North America millions of Monarchs migrate annually over a
distance of 2000 miles ( 3200km ) between their breeding territories
in Canada and their southern over-wintering grounds in Mexico.
Tagging of individual butterflies has shown that
they regularly cover distances of up to 1100 miles in just a few days.
Each autumn as the climate cools in North America, vast numbers fly
south and channel into a few forested areas in the Mexican Highlands.
During the winter months, fir trees in the tiny El Rosario sanctuary
become festooned with millions of Monarchs. They totally cover the
leaves, branches and trunks, sometimes even causing trees to fall
under their weight.
In February & March they awaken from hibernation and the air becomes a
swirling mass of orange and black as tens of thousands of Monarchs
take to the air. As the days get warmer they start to filter out of
the sanctuaries and begin their return journey northwards. The females
pause to lay eggs as they travel, creating temporary colonies along
the route. The progeny also migrate north, laying their own eggs. Most
of the original butterflies probably perish during the return journey,
but there is evidence to show that some manage to return to the
original breeding areas in the north.
It is little known that these amazing butterflies also regularly
overwinter in small numbers in arid desert locations such as Saline
valley in California - a moon-crater shaped valley about midway
between Mount Whitney and Death Valley in the Mojave Desert.
Monarchs regularly survive the winter there despite the very low
daytime humidity ( 5-25% ), scant winter rainfall and the fact the
only evergreen vegetation in mid and late winter are bushes such as
tamarisk, mulefat and creosote. One problem with the Saline Valley
habitats however is that once every five years or so, overnight
temperatures drop several degrees below zero, and freeze most or all
of the Monarchs.
Monarch's annual migration is controlled by a "time-compensated sun
compass" that depends on light receptors and a circadian clock, both
of which are built into their antennae. The circadian clock employs
rhythms of biochemical, physiological or behavioural processes which
control daily, seasonal and annual activities - including migration.
When scientists removed the antennae from one group of Monarchs they
flew strongly but in random directions, but a control group with
their antennae intact all flew in the same direction - their
south-westerly migration route. In another experiment the antennae
of some were painted with black enamel, and these butterflies when
placed in a flight simulator all flew together, but in the "wrong"
direction compared to their normal migration route. Another group
had their antennae painted with transparent paint, and these all
migrated together in the right direction.
Because of its
migratory nature the Monarch can be found in virtually any habitat
, including grasslands & prairies, deciduous temperate forest,
montane pine forest, sub-tropical rainforest, coastal habitats,
deserts, parks, gardens, cities etc. It can be found at elevations
between sea-level and at least 3400 metres. The butterflies can also
be seen out at sea, and often settle on ships.
Monarchs will breed
almost anywhere where the larval foodplants are available, typically
in fields, meadows, forest glades and roadside habitats at
elevations between sea level and about 1000m.
egg is shaped like a tall dome, straw coloured, and covered in
vertical keels, each linked by numerous small horizontal ridges. It
is laid singly on the underside of leaves of the foodplants which
are almost invariably Asclepias but
also include Calotropis ( Apocynaceae
when fully grown is white, with each segment marked with narrow
black and yellow vertical bands. The 2nd thoracic segment and 8th
abdominal segment each bear a pair of black whip-like protuberances.
Caterpillars are often parasitised by a tachinid fly
foodplants Asclepias contain
cardenolides - toxins which can induce cardiac arrest in small
vertebrates. The toxins are sequestered by the caterpillars, and
passed on to the adult butterflies which utilize them for defence
against insectivorous birds, reptiles and rodents.
The pale green
chrysalis is plump and barrel-shaped, with the abdominal segments
compressed, forming a dome. At its widest point there is a narrow
abdominal band studded with yellow and black dots. The chrysalis is
suspended by a stout cremaster from stems on or near the foodplants.
have a powerful but fluttering flight, interspersed with periods of
soaring and gliding in wide circles as they fly from one clump of
flowers to another. They settle frequently to nectar at
place in late morning, at which time the male pursues the female in
flight, nudging and cajoling her until she settles, typically on a
bush, where copulation takes place.