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Rhopalocer
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Butterfly
· A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes 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 belong to the order lepidoptera. There exist approximately 160,000 different species of butterflies in the world! They are an extremely diverse group when compared with the 2000 species of praying mantids, for example! Butterflies are found worldwide, even above the Arctic Circle, but they do not occur on Antarctica.
Butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. Butterflies comprise the true butterflies (superfamily Papilionoidea), the skippers (superfamilyHesperioidea) and the moth-butterflies (superfamily Hedyloidea). All the many other families within the Lepidoptera are referred to as moths. The earliest known butterfly fossils date to the mid Eocene epoch, 40–50 million years ago.
Life cycle of a butterfly
Butterflies undergo complete metamorphosis; this means the early stages of life do not resemble the adult life stage at all. Butterflies are always born as caterpillars. Tiny caterpillars hatch from small eggs. Immediately after hatching they will start to eat leaves of specific plants (their host plants). The caterpillar will grow, but because it has a rigid outer skeleton (their skin provides rigidity, like our inner skeleton) it has to shed its skin to be able to grow. Most species shed their skin four times when in their caterpillar stage. Each time the caterpillar sheds its skin it will grow, and sometimes it will also have different colors after its molt. When the caterpillar reaches its final caterpillar life stage, it will make a cocoon with silk that it produces with its mouth. It will completely cover itself in this silk, making a protective cocoon. Inside this cocoon the caterpillar will shed its skin again, changing into a pupa. Inside the pupa the caterpillar transforms into a butterfly. When it is finished, the butterfly will open the cocoon and sit close to it to inflate its wings. The butterfly will first pump body fluids through its flat wings, making them expand. Then it will replace the fluid with air and lets its wings dry. After that, the butterfly is ready to fly off!
Eggs 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 almost invariably 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.
The senses of butterflies and caterpillars
Butterflies have all the sense we have (sight, smell, hearing, touch and taste), but they rely mostly on smell, touch and taste. Their sense of smell is not located in their nose (they do not have one), but is located in their antennae and even their feet! Butterflies also taste with their feet, stepping on nector or host plants to taste if this is appropriate food for them or their offspring. The other senses of a butterfly are not well developed but serve specific functions very well (e.g. sight = escape from predators and finding of flowers, but no detail and no stereo-vision).Caterpillars also have all senses, but they probably have them even less developed than butterflies. This is because a caterpillar generally can not do more than eat and walk at a very slow pace. Excellent senses will not help it to perform better. They use their sense of smell to identify food plants.
Wing development Wings or wing pads are not visible on the outside of the larva, but when larvae are dissected, tiny developing wing disks can be found on the second and third thoracic segments, in place of the spiracles that are apparent on abdominal segments. Wing disks develop in association with a trachea that runs along the base of the wing, and are surrounded by a thin peripodial membrane, which is linked to the outer epidermis of the larva by a tiny duct.
Wing disks are very small until the last larval instar, when they increase dramatically in size, are invaded by branching tracheae from the wing base that precede the formation of the wing veins, and begin to develop patterns associated with several landmarks of the wing.
Pupa
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 larva transforms into a pupa by anchoring itself to a substrate 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.
Adult or imago
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 (see photo). 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.
Habits
Butterflies use their antennae to sense the air for wind and scents. The antennae come in various shapes and colours; the hesperids have a pointed angle or hook to the antennae, while most other families show knobbed antennae. The antennae are richly covered with sensory organs known assensillae. A butterfly's sense of taste, 200 times stronger than humans, is coordinated by chemoreceptors on the tarsi, or feet, which work only on contact, and are used to determine whether an egg-laying insect's offspring will be able to feed on a leaf before eggs are laid on it. Many butterflies use chemical signals, pheromones, and specialized scent scales (androconia) and other structures (coremata or "hair pencils" in the Danaidae) are developed in some species. 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. 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 more common 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.
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