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The butterfly
lifecycle
1 - Egg
- anatomy, oviposition
2 - Caterpillar
- anatomy
3
- Caterpillar
- hatching, feeding and development
4
- Caterpillar
- cannibals, carnivores and myrmecophiles
5
- Caterpillar
- survival mechanisms,
armature, camouflage / disguise
6
- Caterpillar
-
co-evolution with plants
7
- Chrysalis
- pupation, metamorphosis
8
- Adult
- emergence, feeding
9
- Adult
- mate location and courtship
10 - Adult
- daily routine, roosting, hibernation, lifespan
Adult
: emergence, feeding
Emergence
Emergence of the adult butterfly or moth from the pupa is
triggered by factors including humidity, temperature, light level
and time of day. Most butterflies emerge shortly after dawn.
The
spiracles of the butterfly within the pupa are linked by short
tubes to the spiracle openings on the pupa shell. Just prior to
emergence air is drawn in through these tubes, enabling the
butterfly to pump up it's body, which causes the shell of the pupa
to split, just behind the head.
The butterfly then
forces it's way out, using it's legs to pull itself clear of the
empty pupal shell. If the pupa was formed within a silken shelter
or cocoon, as is the case e.g. with most Hesperiidae species, the
butterfly first ejects solvents from the proboscis. These soften
the silk enough to allow it to push it's way out.
Eueides lybia,
newly emerged from chrysalis, Rio Madre de Dios, Peru ©
Adrian Hoskins
Having emerged and
settled into position, the insect then spends several minutes
hanging virtually
motionless. During this time it pumps fluids into the wing veins,
causing the wings to expand to their full size.
After drying the wings, and before taking their first flight,
butterflies and moths expel the metabolic waste product meconium
from their abdomens, in the form of a pinkish liquid. Male
butterflies
usually fly off as soon as their wings are hardened, but females
of many species tend to stay within a few metres of the emergence
site until mated.
Sex ratios
It is often
claimed that more male butterflies emerge than females. The most
quoted example is of Rajah Brooke's Birdwing
Trogonoptera brookiana whose males are sometimes stated to
outnumber females by a ratio of as much as 10:1. These claims
however are caused by sampling inadequacies - females of most
species are more secretive in behaviour, better camouflaged, and
tend to spend most of their lives in habitats that are less
accessible to observers, e.g. in the forest canopy. Males on the
other hand tend to be more colourful and are considerably more
visible in their behaviour, e.g. males of
brookiana and many other species habitually aggregate in
large numbers to imbibe moisture from muddy ground. Captive
breeding experiments with brookiana
and hundreds of other species have proven that both sexes actually
emerge in similar numbers.
In most species
males emerge at least a day or two before females. The explanation
usually given for this is that females usually mate on the day
they emerge, so it is advantageous if there are already plenty of
males available to them. Another factor not usually
mentioned in literature is that males of some species are not
capable of mating until they are 2-3 days old. This is because
they need to feed in order to accumulate alkaloids that are vital
to reproduction. Well known examples of this include the
Purple Emperor
whose males feed at dung,
Swordtails and
Daggerwings
which feed at urine,
and
Glasswings such as
Pteronymia sao
which feed on decomposing plant material. The latter derive
pyrrolizidine alkaloids from the plants, which are used in the
production of pheromones and defensive toxins, as well as for
reproductive purposes.
Feeding behaviour
Males of many tropical species are regularly observed imbibing
dissolved minerals from damp mud, bird droppings, aphid secretions,
sap runs, or even from carrion. The minerals are later passed to the
females during copulation, and may contain vital nutrients necessary
for the production of fertile eggs.
In temperate regions both sexes of most species
feed primarily at nectar, but males of several species, e.g.
Apatura iris,
Lysandra coridon, Pyrgus alveus,
Thymelicus lineola
and
Mellicta athalia
commonly imbibe mineralised moisture, or visit dung.
Certain members of the subfamily Heliconiinae are unusual in that
their females use nectar to dissolve pollen which they collect from
rainforest flowers. Studies by Gilbert of captive
Heliconius
ethilla in Trinidad have shown that females deprived of
pollen only lay about 15% of the number of eggs laid by females that
have access to pollen. The pollen provides nutrients that cannot be
sequestered from other sources, and contributes greatly to the
longevity of the butterflies. They have been recorded as living for
up to 8 months as adults - most other tropical species live for only
a few days.
Heliconius xanthocles, sequestering pollen from
Psychotia
'hotlips' flowers
© Adrian Hoskins
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