Scales are present on the bodies of various insects. A notable example are the Lepidoptera, the insect order comprising moths and butterflies, which have scales on their wings and on the head, parts of the thorax and abdomen, and parts of the genitalia. The name is derived from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

λεπίδος (scale) and πτερόν (wing).Scoble, M.J. (2005). ''The Lepidoptera: Form, Function, and Diversity''. Page 63. Accessed through Google books on 21 Aug 200

/ref> The

Trichoptera The caddisflies (order Trichoptera) are a group of insects with aquatic larvae and terrestrial adults. There are approximately 14,500 described species, most of which can be divided into the suborders Integripalpia and Annulipalpia on the basis ...

(caddisflies) which are a sister group of the Lepidoptera have scales, but also possess caudal cerci on the abdomen, a feature absent in the Lepidoptera.Powell, Jerry A. Lepidoptera (pp. 631-664) in Resh, V. H. & R. T. Cardé (Editors) 2003. Encyclopedia of Insects. Academic Press. Beetles of family

Dermestidae Dermestidae are a family of Coleoptera that are commonly referred to as skin beetles or carpet beetles. Other common names include larder beetles, hide or leather beetles, and khapra beetles. There are over 1,800 species described. Dermestids ha ...

also commonly have scales. Within the dipteran infraorder

Culicomorpha The Culicomorpha are an infraorder of Nematocera, including mosquitoes, black flies, and several extant and extinct families of insects. They originated 176 million years ago, in the Triassic period. There are phylogenetic patterns that are used ...

, possession of a scale fringe on the posterior margin of the forewings is a proposed

synapomorphy In phylogenetics, an apomorphy (or derived trait) is a novel Phenotypic trait, character or character state that has evolution, evolved from its ancestral form (or Plesiomorphy and symplesiomorphy, plesiomorphy). A synapomorphy is an apomorphy sh ...

Corethrellidae Corethrellidae are a family of biting midges, small flying insects belonging to the order Diptera, females of which feed on the blood of frogs. The members of the family are sometimes known as frog-biting midges. The family currently consists of ...

Chaoboridae Chaoboridae, commonly known as phantom midges or glassworms, is a family of fairly common midges with a cosmopolitan distribution. They are closely related to the Corethrellidae and Chironomidae; the adults are differentiated through peculiariti ...

and

Culicidae Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...

. Many

Zygentoma Zygentoma are an order in the class Insecta, and consist of about 550 known species. The Zygentoma include the so-called silverfish or fishmoths, and the firebrats. A conspicuous feature of the order are the three long caudal filaments. The t ...

and

Archaeognatha The Archaeognatha are an order of apterygotes, known by various common names such as jumping bristletails. Among extant insect taxa they are some of the most evolutionarily primitive; they appeared in the Middle Devonian period at about the sa ...

have scales on their bodies, whose iridescent appearance gives certain Zygentoma the common name of silverfish.

Morphology

Lepidoptera

The morphology of lepidopteran scales has been studied by Downey & Allyn (1975) and scales have been classified into three groups, namely: * Hair-like or piliform. * Blade-like or lamellar. * Other variable forms. Primitive moths (non-Glossata and Eriocranidae) have 'solid' scales which are imperforate, i.e., they lack a lumen. As per Scoble (2005):

Structure

Though there is great diversity in scale form, they are structured similarly. The body or 'blade' of a typical scale consists of an upper and lower lamina. The surface of the lower lamina is smooth whereas the structure of the upper lamina is structured and intricate. Scales are attached to the substrate by a stalk or 'pedicel'. The scales cling somewhat loosely to the wing and come off easily without harming the insect.

Colour

The colouration of butterfly wings is created by the scales which are pigmented with

melanin Melanin (; ) is a family of biomolecules organized as oligomers or polymers, which among other functions provide the pigments of many organisms. Melanin pigments are produced in a specialized group of cells known as melanocytes. There are ...

s that give them blacks and browns, but blues, greens, reds and iridescence are usually created not by pigments but the microstructure of the scales. This

structural coloration Structural coloration in animals, and a few plants, is the production of colour by microscopically structured surfaces fine enough to interfere with visible light instead of Biological pigment, pigments, although some structural coloration occu ...

is the result of coherent scattering of light by the

photonic crystal A photonic crystal is an optical nanostructure in which the refractive index changes periodically. This affects the propagation of light in the same way that the structure of Crystal structure, natural crystals gives rise to X-ray crystallograp ...

nature of the scales.

Function

Scales play an important part in the natural history of Lepidoptera. Scales enable development of vivid or indistinct patterns which help the organism protect itself by concealment and

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

mimicry In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. In the simples ...

and warning. Besides providing

insulation Insulation may refer to: Thermal * Thermal insulation, use of materials to reduce rates of heat transfer ** List of insulation materials ** Building insulation, thermal insulation added to buildings for comfort and energy efficiency *** Insulated ...

, dark patterns on wings provided by dark colour scales would allow sunlight to be absorbed and thus probably have a role to play in thermoregulation. Bright and distinctive colour patterns in butterflies which are distasteful to predators help communicate their

aposematism Aposematism is the Advertising in biology, advertising by an animal, whether terrestrial or marine, to potential predation, predators that it is not worth attacking or eating. This unprofitability may consist of any defenses which make the pr ...

(toxicity or inedibility) thus preventing a predator from preying on it. In

Batesian mimicry Batesian mimicry is a form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both. It is named after the English naturalist Henry Walter Bates, who worked on butt ...

, wing colour patterns help edible Lepidopterans mimic inedible models while in

Müllerian mimicry Müllerian mimicry is a natural phenomenon in which two or more well-defended species, often foul-tasting and sharing common predators, have come to mimicry, mimic each other's honest signal, honest aposematism, warning signals, to their mutuali ...

inedible butterflies resemble each other to reduce the numbers of individuals sampled by predators. Scales possibly evolved initially for providing insulation. Scales on the thorax and other parts of the body probably contribute to maintaining the high body temperatures required during flight. The 'solid' scales of basal moths are however not as efficient as those of their more advanced relatives as the presence of a lumen adds air layers and increases the insulation value. Young adults of

myrmecophilous thumb , Myrmecophilous aphids being tended by ants Myrmecophily ( , ) consists of positive, mutualistic, interspecies associations between ants and a variety of other organisms, such as plants, other arthropods, and fungi. It may also incl ...

Lepidoptera escape from ant nests by virtue of the deciduous waxy scales with which they are covered when born. These scales rub off and stick on the ants as they make their way out of the nest after hatching. Scales greatly reduce fatalities among Lepidoptera after flying into spiderwebs. The detachable scales pull away freely and enable the insect to escape. (Forsyth 1992:12)

Thomas Eisner Thomas Eisner (June 25, 1929 – March 25, 2011) was a German-American entomologist and ecologist, known as the "father of chemical ecology." He was a Jacob Gould Schurman Professor of Chemical Ecology at Cornell University, and director of the ...

tested spiderwebs' effectiveness by dropping various insects onto the webs. Moths were consistently able to escape, and all left impact spots where scales had stuck to the web. Eisner found these spots to be common. (Eisner 2003:218-220) Scales also help increase the

lift to drag ratio In aerodynamics, the lift-to-drag ratio (or L/D ratio) is the lift generated by an aerodynamic body such as an aerofoil or aircraft, divided by the aerodynamic drag caused by moving through air. It describes the aerodynamic efficiency under give ...

in gliding flight. Successive close-ups of the scales of a Peacock wing

Zygentoma and Archaeognatha

The orders Zygentoma and Archaeognatha were formerly united as suborders of

Thysanura Thysanura is the now Deprecation, deprecated name of what was, for over a century, recognised as an Order (biology), order in the Class (biology), class Insecta. The two constituent groups within the former order, the Archaeognatha (jumping bristle ...

, but were found to not have a sister relationship and were consequently elevated as orders. Scales are not present in the first instar in either order, appearing after one or more molts—two in Archaeognatha. The extent of scaling varies between taxa, with at least the three terminal filaments, tergites and abdominal coxites bearing scales in known Archaeognatha. Certain families of Zygentoma are scaleless.

Structure

The structure of scales differs between the two orders; Zygentoma scales have a membrane with raised ribs on their upper surface, while Archaeognatha scales contain a porous lumen formed by upper and lower plates.

Function

The scales of Zygentoma and Archaeognatha may serve anti-predator{{cite book, title=The Audubon Society Field Guide to North American Insects and Spiders, last1=Milne, first1=Lorus, last2=Milne, first2=Margery, others=Visual key by Susan Rayfield, year=1980, publisher=Alfred A. Knopf, Inc., isbn=0-394-50763-0, page=352 and mechanosensory functions.

References

Lepidopterology Insect anatomy

Morphology

Lepidoptera

Structure

Colour

Function

Zygentoma and Archaeognatha

Structure

Function

See also

References