Butterfly Ef

[Channing Arther]

Butterfliesare winged insects from the lepidopteran suborder Rhopalocera, characterized by large, often brightly coloured wings that often fold together when at rest, and a conspicuous, fluttering flight. The group comprises the superfamilies Hedyloidea (moth-butterflies in the Americas) and Papilionoidea (all others). The oldest butterfly fossils have been dated to the Paleocene, about 56 million years ago, though they likely originated in the Late Cretaceous, about 101 million years ago.[1]

Butterflies have a four-stage life cycle, and like other holometabolous insects they undergo complete metamorphosis.[2] Winged adults lay eggs on the food plant on which their larvae, known as caterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed, pupate in a chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out, expands its wings to dry, and flies off.

Some butterflies, especially in the tropics, have several generations in a year, while others have a single generation, and a few in cold locations may take several years to pass through their entire life cycle.[3]

Butterflies are often polymorphic, and many species make use of camouflage, mimicry, and aposematism to evade their predators.[4] Some, like the monarch and the painted lady, migrate over long distances. Many butterflies are attacked by parasites or parasitoids, including wasps, protozoans, flies, and other invertebrates, or are preyed upon by other organisms. Some species are pests because in their larval stages they can damage domestic crops or trees; other species are agents of pollination of some plants. Larvae of a few butterflies (e.g., harvesters) eat harmful insects, and a few are predators of ants, while others live as mutualists in association with ants. Culturally, butterflies are a popular motif in the visual and literary arts. The Smithsonian Institution says "butterflies are certainly one of the most appealing creatures in nature".[5]

The Oxford English Dictionary derives the word straightforwardly from Old English butorflēoge, butter-fly; similar names in Old Dutch and Old High German show that the name is ancient, but modern Dutch and German use different words (vlinder and Schmetterling) and the common name often varies substantially between otherwise closely related languages. A possible source of the name is the bright yellow male of the brimstone (Gonepteryx rhamni); another is that butterflies were on the wing in meadows during the spring and summer butter season while the grass was growing.[6][7]

The earliest Lepidoptera fossils date to the Triassic-Jurassic boundary, around 200 million years ago.[8] Butterflies evolved from moths, so while the butterflies are monophyletic (forming a single clade), the moths are not. The oldest known butterfly is Protocoeliades kristenseni from the Palaeocene aged Fur Formation of Denmark, approximately 55 million years old, which belongs to the family Hesperiidae (skippers).[9] Molecular clock estimates suggest that butterflies originated sometime in the Late Cretaceous, but only significantly diversified during the Cenozoic,[10][1] with one study suggesting a North American origin for the group.[1] The oldest American butterfly is the Late Eocene Prodryas persephone from the Florissant Fossil Beds,[11][12] approximately 34 million years old.[13]

Butterflies are scientifically classified in the macrolepidopteran suborder clade Rhopalocera from the order Lepidoptera, which also includes moths.[citation needed] Traditionally, butterflies have been divided into the superfamily Papilionoidea excluding the smaller groups of the Hesperiidae (skippers) and the more moth-like Hedylidae of America. Phylogenetic analysis suggests that the traditional Papilionoidea is paraphyletic with respect to the other two groups, so they should both be included within Papilionoidea, to form a single butterfly group, thereby synonymous with the clade Rhopalocera.[14][15]

As in all insects, the body is divided into three sections: the head, thorax, and abdomen. The thorax is composed of three segments, each with a pair of legs. In most families of butterfly the antennae are clubbed, unlike those of moths which may be threadlike or feathery. The long proboscis can be coiled when not in use for sipping nectar from flowers.[20]

Nearly all butterflies are diurnal, have relatively bright colours, and hold their wings vertically above their bodies when at rest, unlike the majority of moths which fly by night, are often cryptically coloured (well camouflaged), and either hold their wings flat (touching the surface on which the moth is standing) or fold them closely over their bodies. Some day-flying moths, such as the hummingbird hawk-moth,[21] are exceptions to these rules.[20][22]

Butterflies are distributed worldwide except Antarctica, totalling some 18,500 species.[24] Of these, 775 are Nearctic; 7,700 Neotropical; 1,575 Palearctic; 3,650 Afrotropical; and 4,800 are distributed across the combined Oriental and Australian/Oceania regions.[24] The monarch butterfly is native to the Americas, but in the nineteenth century or before, spread across the world, and is now found in Australia, New Zealand, other parts of Oceania, and the Iberian Peninsula. It is not clear how it dispersed; adults may have been blown by the wind or larvae or pupae may have been accidentally transported by humans, but the presence of suitable host plants in their new environment was a necessity for their successful establishment.[25]

Butterflies navigate using a time-compensated sun compass. They can see polarized light and therefore orient even in cloudy conditions. The polarized light near the ultraviolet spectrum appears to be particularly important.[32][33] Many migratory butterflies live in semi-arid areas where breeding seasons are short.[34] The life histories of their host plants also influence butterfly behaviour.[35]

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.[36] The Melissa Arctic (Oeneis melissa) overwinters twice as a caterpillar.[37] 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.[38]

Courtship is often aerial and often involves pheromones. Butterflies then land on the ground or on a perch to mate.[20] Copulation takes place tail-to-tail and may last from minutes to hours. Simple photoreceptor cells located at the genitals are important for this and other adult behaviours.[39] The male passes a spermatophore to the female; to reduce sperm competition, he may cover her with his scent, or in some species such as the Apollos (Parnassius) plugs her genital opening to prevent her from mating again.[40]

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 eggs vary greatly in size and shape between species, but are usually upright and finely sculptured. Some species lay eggs singly, others in batches. Many females produce between one hundred and two hundred eggs.[41]

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 has been little researched but in the case of Pieris brassicae, it begins as a pale yellow granular secretion containing acidophilic proteins. This is viscous and darkens when exposed to air, becoming a water-insoluble, rubbery material which soon sets solid.[42] Butterflies in the genus Agathymus do not fix their eggs to a leaf; instead, the newly laid eggs fall to the base of the plant.[43]

Eggs are almost invariably laid on plants. Each species of butterfly has its own host plant 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.[44] In some species, such as the great spangled fritillary, the eggs are deposited close to but not on the food plant. This most likely happens when the egg overwinters before hatching and where the host plant loses its leaves in winter, as do violets in this example.[45]

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.[46] Some temperate region butterflies, such as the Camberwell beauty, lay their eggs in the spring and have them hatch in the summer.[47]

Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time searching for and eating food. Although most caterpillars are herbivorous, a few species are predators: Spalgis epius eats scale insects,[48] while lycaenids such as Liphyra brassolis are myrmecophilous, eating ant larvae.[49]

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.[50][51] The ants provide some degree of protection to these larvae and they in turn gather honeydew secretions. Large blue (Phengaris arion) caterpillars trick Myrmica ants into taking them back to the ant colony where they feed on the ant eggs and larvae in a parasitic relationship.[52]

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