A
butterfly is a mainly day-flying
insect of the
order Lepidoptera, the butterflies and
moths. Like other
holometabolous insects, the butterfly's
life cycle consists of four parts,
egg,
larva,
pupa and adult. Most species are
diurnal. Butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. Butterflies comprise the
true butterflies (superfamily
Papilionoidea), the
skippers (superfamily
Hesperioidea) and the
moth-butterflies (superfamily
Hedyloidea). All the many other families within the Lepidoptera are referred to as
moths.
Butterflies exhibit
polymorphism,
mimicry and
aposematism. Some, like the
Monarch, will
migrate over long distances. Some butterflies have evolved symbiotic and parasitic relationships with social insects such as ants. Some species are pests because in their larval stages they can damage domestic crops or trees; however, some species are agents of
pollination of some plants, and caterpillars of a few butterflies (e.g.,
Harvesters) eat harmful insects. Culturally, butterflies are a popular motif in the visual and literary arts.
Life cycle
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.
Butterflies may have one or more broods per year. The number of generations per year varies from temperate to tropical regions with tropical regions showing a trend towards
multivoltinism.
Egg
Butterfly eggs are protected by 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 of butterfly are restricted to just one species of plant, others use a range of plant species, often including 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 (resting) stage, and the hatching may take place only in spring. Other butterflies may lay their eggs in the spring and have them hatch in the summer. These butterflies are usually northern species, such as the
Mourning Cloak (Camberwell Beauty) and the
Large and
Small Tortoiseshell butterflies.
Caterpillars
Butterfly larvae, or
caterpillars, 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
mutual associations with ants. They communicate with the ants using vibrations that are transmitted through the substrate as well as using chemical signals.
[2][3] 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 tough outer layer made of a mixture of
chitin and specialized
proteins, is released from the softer
epidermis beneath, 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 expands, before rapidly hardening and developing pigment. 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 "arms race" has led to the coevolution of insects and their host plants.
http://en.wikipedia.org/wiki/Butterfly
