Modules:

• Integument
• Respiration
• Circulation
• Metamorphosis
• Hormones
• Moulting
• Dormancy
• Circadian Rhythms
• Feeding & Nutrition
• Excretion & Water Balance
• Sensing touch, movement & sound
• Sensing taste & odours
• Olfactory Orientation
• Eyes & Vision
• Neural Integration
• Flight & locomotion
• Memory & Learning
• Reproduction
• Semiochemicals
• Bioluminescence
• Thermoregulation
• Insecticides mode of action

Integument Modifications: Colours & Camouflage

Image courtesy of Alex Wild Photography with permission

Physical and pigmentary colours

The cuticle of insects is often brown or black but can be a range of colours as seen in butterflies, moths, ladybeetles and the reds and golds of some jewel beetles. Colour is achieved through a number of mechanisms. Light waves can interfere with one another as they bounce off cuticle which has a grating or fine striation. These are called interference colours and produce iridescence and ultraviolet colours. They are also called physical or structural colours.
Pigmentary colours are due to chemicals that absorb some wavelengths and reflect others. Read Chapter 25, parts 25.1 to 25.6 in Chapman.

Interference colours

The cuticle of insects is often brown or black but can be a range of colours as seen in butterflies, moths, ladybeetles and the reds and golds of some jewel beetles. Colour is achieved through a number of mechanisms. Light waves can interfere with one another as they bounce off cuticle which has a grating or fine striation. These are called interference colours and produce iridescence and ultraviolet colours. Butterfly and moth scales have such patterns.

Moth scales under the scanning electron microscope. The fine pits and grooves produce interference colours. [Image: BW Cribb]	Informative external site featuring scales and eye facets. Diagram of microstructure of insect wing scales Below: a movie from the series NatureTech, Smithsonian channel, explaining the shape of the butterfly scale

	Left: A movie about the role of cuticle in insect camouflage, featuring preying mantids, leaf-mimicking insects. It also features a beetle found in the Namib desert whose cuticle is adapted for condensing water from fog, and channelling it into the beetle’s mouth. Last, a grasshopper is shown moulting.
Movie: From NatureTech, Smithsonian Channel

Light scattering and gathering Colours can also be produced by light scattering that relies on the degree of cuticular roughness relative to the wavelength of impinging light. Whites are produced by structures larger than the wavelength of light whereas blues require irregularities that reflect only short wavelengths. Watch the video at right to see how microsculpturing of a moth’s eye helps it absorb all light. Check out this link to see how nanotechnology is trying to produce the same outcomes.

Pigments

The third mechanism for producing colour is pigment. Chemicals with colour can be found in secretions onto the cuticle, within the cuticle, or in the epidermis or fat body.
A range of chemicals are involved: carotenoids and flavonoids can produce yellows, tetrapyrrholes provide reds, blues and greens, melanins produce blacks.

Hemoglobin, that gives our blood its red colour, is relatively rare in insects. Some aquatic insects that frequent environments where oxygen is limiting have evolved hemoglobin pigments and show a red colouration.

Read about physiological colour change in Chapman section 25.5

Herbert A. "Joe" Pase III, Texas Forest Service, Bugwood.org

 

Go on to the next section on Surface Modifications

Return to Integument Part 1: Structure and function