-by-Carl-Spitzweg-(1840).jpg) A
butterfly is a insect of the order Lepidoptera,
They are notable for their unusual life cycle with a larval caterpillar
stage, an inactive pupal stage and a spectacular metamorphosis into a
familiar and colourful winged adult form.
The diverse patterns formed by their brightly coloured wings and their
erratic-yetgraceful flight have made butterfly watching a popular hobby.
The Old English word for butterfly was buttorfleoge apparently because
butterflies were thought to steal milk.
A similar word occurs in Dutch and German originating from the same
belief.
This is believed to have led to the evolution of its present name form -
butterfly.
The five families of true butterflies usually recognized in theer
Schmetterlingsjager (The butterfly hunter) by Carl Spitzweg (1840)
*Papilionoidea are:
* Family Papilionidae, the Swallowtails and Birdwings
* Family Pieridae, the Whites and Yellows
* Family Lycaenidae, the Blues and Coppers, also called the
Gossamer-Winged Butterflies
* Family Riodinidae, the Metalmark butterflies
* Family Nymphalidae, the Brush-footed butterflies.
The four stages in the lifecycle of a butterfly:
* Egg * Larva, known as a caterpillar
* Pupa (chrysalis)
* Adult butterfly (imago)
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 and egg
stages and thereby survive winters.
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. Each species of butterfly has its own
hostplant range and
while some species are restricted to just one species, others use a
range of plant species,
often members of a common family.
The egg stage lasts a few weeks in most butterflies but eggs laid close
to winter especially
in temperate regions go through a diapause stage and the hatching may
take place only in
spring.
Larvae, or caterpillars, are multi-legged eating machines. They consume
plant leaves and
spend practically all of their time in search of food. Although most
caterpillars are herbivorous,
a few species such as Spalgis epius and Liphyra brassolis are
entomophagous (insect
eating). Some larvae, especially those of the Lycaenidae form
mutualistic associations with
ants. They communicate with the ants using vibrations that are
transmitted through the
substrate as well as using chemical signals.The ants provide some degree
of protection to
these larvae and they in turn gather honeydew secretions.
Caterpillars mature through a series of stages, called instars. Near the
end of each instar,
the larva undergoes a process called apolysis, in which the cuticle, a
mixture of chitin and
specialized proteins, is released from the epidermis and the epidermis
begins to form a new
cuticle beneath. At the end of each instar, the larva moults the old
cuticle, and the new
cuticle rapidly hardens and pigments. Development of butterfly wing
patterns begins by the
last larval instar.
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.
Some caterpillars have the ability to inflate parts of their head to
appear snake-like. Many
have false eye-spots to enhance this effect. Some caterpillars have
special structures
called osmeteria which are everted to produce smelly chemicals. These
are used in defense.
Host plants often have toxic substances in them and caterpillars are
able to sequester
these substances and retain them into the adult stage. This helps making
them unpalatable
to birds and other predators. Such unpalatibility is advertised using
bright red, orange,
black or white warning colours. The toxic chemicals in plants are often
evolved specifically
to prevent them from being eaten by insects. Insects in turn develop
countermeasures or
make use of these toxins for their own survival. This evolutionary arms
race has lead to
coevolution in the insects and their host plants.
Near pupation, the wings are forced outside the epidermis under pressure
from the hemolymph,
and although they are initially quite flexible and fragile, by the time
the pupa breaks
free of the larval cuticle they have adhered tightly to the outer
cuticle of the pupa (in
obtect pupae). Within hours, the wings form a cuticle so hard and
well-joined to the body
that pupae can be picked up and handled without damage to the wings.
When the larva is fully grown the larva stops feeding and begins
"wandering" in the quest of
a suitable pupation site, often the underside of a leaf.
The larva transforms into a pupa (or chrysalis) by anchoring itself to a
subtrate and moulting
for the last time. 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. If one wing is surgically removed early on, the other
three will grow to a larger
size. In the pupa, the wing forms a structure that becomes compressed
from top to bottom
and pleated from proximal to distal ends as it grows, so that it can
rapidly be unfolded to its
full adult size.
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 ,but, unlike moths,
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.
Butterflies feed primarily on nectar from flowers. Some also derive
nourishment from
pollen, tree sap, rotting fruit, dung, and dissolved minerals in wet
sand or dirt. Butterflies
play an important ecological role as pollinators.
As adults, butterflies consume only liquids and these are sucked by
means of their proboscis.
They feed on nectar from flowers and also sip water from damp patches.
This they do
for water, for energy from sugars in nectar and for sodium and other
minerals which are
vital for their reproduction. Several species of butterflies need more
sodium than provided
by nectar. They are attracted to sodium in salt and they sometimes land
on people,
attracted by human sweat. Besides damp patches, some butterflies also
visit dung, rotting
fruit or carcasses to obtain minerals and nutrients. In many species,
this behaviour is
restricted to the males and studies have suggested that the nutrients
collected are provided
as a nuptial gift along with the spermatophore during mating.
Butterflies sense the air for scents, wind and nectar using their
antennae. The antennae
come in various shapes and colours.The antennae are richly covered with
sensillae. Chemoreceptors
are also present on the tarsi and these work only on contact. Many
butterflies use
chemical signals, pheromones, and specialized scent scales (androconia)
.
Many butterflies, such as the Monarch butterfly, are migratory and
capable of long distance
flights. They migrate during the day and use the sun to orient
themselves. They also perceive
polarized light and use it for orientation when the sun is hidden.
Many species of butterfly maintain territories and actively chase other
species or individuals
that may stray into them.
Many species of butterfly maintain territories and actively chase other
species or individuals that may stray into them. Some species will bask
or perch on chosen perches. The flight styles of butterflies are often
characteristic and some species have courtship flight displays. Basking
is an activity which is commoner in the cooler hours of the morning.
Many species will orient themselves to gather heat from the sun. Some
species have evolved dark wingbases to help in gathering more heat and
this is especially evident in alpine forms. Butterflies are threatened
in their early stages by parasitoids and in all stages by predators,
diseases and environmental factors. They protect themselves by a variety
of means. Chemical defenses are widespread and are often based on
chemicals of plant origin. In many cases the plants themselves have
evolved these toxic substances to reduce attack to them. These defense
mechanisms are effective only if they are also well advertised. Many
unpalatable butterflies are brightly colored. This has led to
unprotected butterflies evolving forms that appear like the unpalatable
butterflie s.
These mimetic forms are usually restricted to the females. Cryptic
coloration is found in many butterflies. Some like the oakleaf butterfly
are remarkable imitations of leaves.As caterpillars, many defend
themselves by freezing and appearing like sticks or branches. Some
papilionid caterpillars resemble bird dropping in their early instars.
Some caterpillars have hairs and bristly structures that provide
protection while others are gregarious and form dense aggregations. Some
species also form associations with ants and gain their protection (See
Myrmecophile). Behavioural defenses include perching and wing positions
to avoid being conspicuous. Some female Nymphalid butterflies are known
to guard their eggs from parasitoid wasps. Eyespots and tails are found
in many lycaenid butterflies and these divert the attention of predators
from the more vital head region. An alternative theory is that these
cause ambush predators such as spiders to approach from the wrong end
and allow for early visual detection. |
