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Butterflies undergo a complete metamorphosis while
going through four different stages:
Egg: The first stage of a butterfly is the
egg which is laid on the leaf of a plant. Butterfly
eggs consist of a hard-ridged outer layer of shell,
called the chorion. This is lined with a thin coating
of wax which prevents the egg from drying out before
the larva has had time to fully develop.
Each egg contains a number of tiny funnel-shaped openings
at one end, called micropyles; the purpose of these
holes is to allow sperm to enter and fertilize the
egg. Butterfly and moth eggs vary greatly in size
between species, but they are all either spherical
or ovate.
Butterfly eggs are fixed to a leaf with a special
glue which hardens rapidly. As it hardens it contracts,
deforming the shape of the egg. This glue is easily
seen surrounding the base of every egg forming a meniscus.
The nature of the glue is unknown and is a suitable
subject for research. The same glue is produced by
a pupa to secure the setae of the cremaster. This
glue is so hard that the silk pad, to which the setae
are glued, cannot be separated. Eggs are usually laid
on plants.
Larva: The larva is the stage that immediately
follows after the egg hatches. Butterfly larvae, or
caterpillars, consume plant leaves and spend practically
all of their time in search of food. It starts feeding
on the leaves and flowers and continues feeding on
them. It undergoes a massive change in growth as well
as shape.
Caterpillars mature through a series of stages called
instars. Butterfly caterpillars have three pairs of
true legs from the thoracic segments and up to 6 pairs
of prolegs arising from the abdominal segments. These
prolegs have rings of tiny hooks called crochets that
help them grip the substrate.
Pupa: It grows into a pupa which is the resting
stage. When the larva is fully grown, hormones such
as prothoracicotropic hormone (PTTH) are produced.
At this point the larva stops feeding and begins "wandering"
in the quest of a suitable pupation site, often the
underside of a leaf.
The chrysalis is usually incapable of movement, although
some species can rapidly move the abdominal segments
or produce sounds to scare potential predators. The
pupal transformation into a butterfly through metamorphosis
has held great appeal to mankind. To transform from
the miniature wings visible on the outside of the
pupa into large structures usable for flight, the
pupal wings undergo rapid mitosis and absorb a great
deal of nutrients.
Adult: This is the final stage, which is the
beautiful flying adult.
The adult, sexually mature, stage of the insect is
known as the imago. As Lepidoptera, butterflies have
four wings that are covered with tiny scales. The
fore and hindwings are not hooked together, permitting
a more graceful flight.
An adult butterfly has six legs, but in the nymphalids,
the first pair is reduced. After it emerges from its
pupal stage, a butterfly cannot fly until the wings
are unfolded. A newly-emerged butterfly needs to spend
some time inflating its wings with blood and letting
them dry, during which time it is extremely vulnerable
to predators. Some butterflies' wings may take up
to three hours to dry while others take about one
hour.
It is a popular belief that butterflies have very
short life spans. However, butterflies in their adult
stage can live from a week to nearly a year depending
on the species. Many species have long larval life
stages while others can remain dormant in their pupal
or egg stages and thereby survive winters.
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