Scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number w ...

are present on the bodies of various insects. A notable example are

Lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...

, the insect order comprising moths and butterflies, which has scales on their wings and also on the head, parts of the thorax and abdomen as well as 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 ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

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, or 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 b ...

(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. Other common names include larder beetle, hide or leather beetles, carpet beetles, and khapra beetles. There are over 1,100 species described. Dermestids have ...

also commonly have scales.Byrd, Jason. Castner, James (2001)
Forensic Entomology: The Utility of Arthropods in Legal Investigations
/ref>

Morphology

The morphology of 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 butterfly.

Colour

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

melanin Melanin (; from el, μέλας, melas, black, dark) is a broad term for a group of natural pigments found in most organisms. Eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino ...

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 pigments, although some structural coloration occurs in combination wi ...

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 natural crystals gives rise to X-ray diffraction and that the atomic ...

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. Often, mimicry f ...

and warning. Besides providing insulation, 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 by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste ...

(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, after his work on ...

, 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 mimic each other's honest warning signals, to their mutual benefit. The benefit to Mülleria ...

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 Myrmecophily ( , ) is the term applied to positive interspecies associations between ants and a variety of other organisms, such as plants, other arthropods, and fungi. Myrmecophily refers to mutualistic associations with ants, though in its ...

Lepidoptera escape from ant's 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 {{ButterflyScaleMicroscopy

References

Lepidopterology Insect anatomy

Morphology

Structure

Colour

Function

See also

References